Pneumatic tire

ABSTRACT

A pneumatic tire includes an inner liner disposed on an inner side of the tire. The inner liner is composed of a polymer sheet made of an elastomer composition containing a SIBS modified copolymer obtained by modifying a styrene block portion of a styrene-isobutylene-styrene triblock copolymer with acid anhydride. In the inner liner, a ratio (Gs/Gb) between an average thickness Gb in a bead region Rb extending from a tire largest width position to a bead toe and an average thickness Gs in a buttress region Rs extending from the tire largest width position to a corresponding position Lu at a belt layer end is 0.30 to 0.75.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.14/353,235 filed on Apr. 21, 2014, which was filed as the National Phaseof PCT International Application No. PCT/JP2012/069159 filed on Jul. 27,2012, which claims the benefit of priority to Japanese Application Nos.2012-032590 filed on Feb. 17, 2012, 2011-270102 filed on Dec. 9, 2011and 2011-245502 filed on Nov. 9, 2011, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to a pneumatic tire including an innerliner.

The present invention relates to a pneumatic tire including an innerliner, and particularly to a pneumatic tire in which flection crackgrowth resulting from repeated flection deformation during travelingwith the tire is prevented in the inner liner, in which air permeabilityresistance and weather resistance are improved.

BACKGROUND ART

In recent years, in response to strong social demands for low fuelconsumption of vehicles, weight reduction for tires has been sought inevery tire members. Weight reduction of an inner liner has also beensought. The inner liner is disposed on the inner side of a tire, andserves to improve air permeability resistance by reducing an amount ofleakage of air (amount of permeating air) from inside to outside of thepneumatic tire.

Currently, a rubber composition for such an inner liner employs, forexample, a rubber blend mainly containing a butyl rubber. The rubberblend contains the butyl rubber by 70 percent by mass to 100 percent bymass, and a natural rubber by 30 percent by mass to 0 percent by mass.In this way, the tire is provided with improved air permeabilityresistance. In addition to butylene, the rubber blend mainly containingthe butyl rubber contains isoprene by approximately 1 percent by mass,which acts with sulfur, vulcanization accelerator, and zinc white toachieve co-crosslinking between molecules with an adjacent rubber layer.In the case of normal blend, the above-described butyl-based rubberneeds to have a thickness of 0.6 mm to 1.0 mm for a tire of a passengercar, and needs to have a thickness of approximately 1.0 mm to 2.0 mm fora tire of a truck/bus. In order to achieve weight reduction of suchtires, polymer which is more excellent in air permeability resistanceand can provide an inner liner layer with a thinner thickness than thebutyl-based rubber has been requested.

There is a conventional technique of using a thermoplastic elastomer forweight reduction of the inner liner layer. With this technique, however,if the thickness is made thinner than an inner liner of butyl rubber, itis difficult to achieve air permeability resistance and weight reductionat the same time. Moreover, making the thinness smaller decreases thestrength of the inner liner, with the result that the inner liner may bebroken due to heat and pressure of a bladder during a vulcanizationstep. Furthermore, in the case of thermoplastic elastomer of lowstrength, cracks are likely to be produced in the inner liner at abuttress portion which is subjected to large repeated shearingdeformation during traveling with the tire.

Conventionally, in order to achieve weight reduction of a tire, it hasbeen proposed to use a film made of a material containing athermoplastic resin, instead of the above-described rubber composition.However, the tire is left outdoor during transportation or display at adealer, and suffers from degradation due to ultraviolet radiation ofsunlight, so that a thermoplastic elastomer deteriorates to cause acrack, resulting in an impression of bad inner appearance. Moreover,since a pneumatic tire is filled with air in its inner space during use,oxygen in the air will permeate the inside of components constitutingthe tire, causing oxidation to progress with time. An adverse influencewill thus be effected on durability of the pneumatic tire. Inparticular, if a crack occurs in the inner liner, an impression of badinner appearance is given to a user. Furthermore, gas barrier propertypartially deteriorates to decrease tire internal pressure.

In addition, during traveling with the tire, large shear strain acts onthe vicinity of a shoulder portion in the inner liner. When the materialcontaining a thermoplastic resin is used as the inner liner, this shearstrain is likely to cause detachment at an adhesion interface betweenthe inner liner and the carcass ply, with the result that air leakagetakes place from the tire, disadvantageously.

Meanwhile, in order to achieve weight reduction of the inner liner, atechnique of employing a thermoplastic elastomer material also has beenproposed. However, it is known that a material, which is made thinner inthickness than the inner liner of butyl rubber and exhibits high airpermeability resistance, is inferior to the inner liner of butyl rubberin view of vulcanization adhesion strength with an insulation rubber ora carcass ply rubber adjacent to the inner liner.

When the inner liner has low vulcanization adhesion strength, air entersbetween the inner liner and the insulation rubber or the carcass rubber,thus resulting in a so-called air-in phenomenon, in which smallballoon-like objects appear. The multiplicity of such small spots in thetire gives a user an impression of bad appearance. In addition, duringtraveling, the air causes detachment to result in cracks in the innerliner. Accordingly, the tire internal pressure is decreased.

Japanese Patent Laying-Open No. 9-019987 (PTD 1) discloses a layer stackfor improving adhesive property between an inner liner layer and arubber layer. By providing adhesion layers on the opposite sides of theinner liner layer, the adhesion layers come into contact with each otherat an overlapping portion of the inner liner layer and are bonded firmlyby heating. Air pressure retainability is thus improved. However, theadhesive layers for the overlapping of the inner liner layer will comeinto contact with the bladder in a heated state during a vulcanizationstep to stick and adhere to the bladder, disadvantageously.

In Japanese Patent No. 2999188 (Japanese Patent Laying-Open No.2000-159936 (PTD 2)), a mixture of a nylon resin having excellent airpermeability resistance and a butyl rubber is produced by dynamiccross-linking, thereby fabricating an inner liner layer having athickness of 100 μm. However, the nylon resin is hard at a roomtemperature, and is therefore not suitable for an inner liner for atire. Further, the mixture produced by dynamic cross-linking is notenough to achieve vulcanization adhesion with a rubber layer. Hence, anadhesive layer for vulcanization is required apart from the inner linerlayer. This results in a complicated structure as an inner liner memberas well as increased number of steps, which is disadvantageous in viewof productivity.

In Japanese Patent Laying-Open No. 2008-024219 (PTD 3), a flexible gasbarrier layer is fabricated by dispersing a maleic anhydride modifiedhydrogenated styrene-ethylene-butadiene-styrene block copolymer in anethylene-vinyl alcohol copolymer having excellent air permeabilityresistance. The layer is sandwiched by thermoplastic polyurethane layersto form a sandwich structure, and a rubber cement (obtained bydissolving a butyl rubber and a natural rubber at 70/30 in toluene) isapplied to a surface to be adhered to the tire rubber, therebyfabricating an inner liner layer. However, the modified ethylene-vinylalcohol copolymer having the flexible resin dispersed therein has lowadhesive strength, and may be detached from the thermoplasticpolyurethane layers. Moreover, although the modified ethylene-vinylalcohol copolymer having flexible resin dispersed therein has flexibleresin dispersed therein, the EVOH of the matrix has poor flectionfatigue resistance, thus resulting in breakage during traveling with thetire. Since the rubber cement is applied to the surface to be adhered tothe tire rubber, a step different from the normal inner liner step isrequired, resulting in degraded productivity.

Japanese Patent Laying-Open No. 2008-174037 (PTD 4) proposes a pneumatictire having, on the inner side of a carcass layer, an air permeationpreventing layer of a thermoplastic elastomer composition containing athermoplastic resin or a thermoplastic resin and an elastomer, in whichan average thickness Gs of the air permeation prevention layer extendingfrom the vicinity of a maximum width end of a belt layer to a tiremaximum width region Ts is made thinner than an average thickness Gf ofthe air permeation preventing layer in a region Tf extending from thetire maximum width to a bead toe, thereby improving flection durability.Such a configuration, however, may cause detachment between a rubberlayer of a carcass ply and the air permeation preventing layer.

To simultaneously achieve suppression of air pressure drop, improvementin durability and improvement in fuel consumption, Japanese PatentLaying-Open No. 2007-291256 (PTD 5) discloses a pneumatic tire formedusing a rubber composition for an inner liner containing ethylene-vinylalcohol copolymer by 15 parts by mass to 30 parts by mass with respectto 100 parts by mass of a rubber component made of a natural rubberand/or a synthetic rubber.

In Japanese Patent Laying-Open No. 2009-298986 (PTD 6), titanium oxideis blended with a blend of a butyl-based rubber and a nylon resin forpreventing ultraviolet degradation. However, besides ultravioletdegradation, durability is disadvantageously decreased by degradation ofnylon resin due to occurrence of radical caused by flection fatigue.

In WO2007/116983 (PTD 7), a light sealing layer in which carbon black isblended with a mold lubricant for preventing ultraviolet degradation ofa thermoplastic elastomer layer is provided on a surface layer. However,due to fluctuations in the step of applying the mold lubricant, the moldlubricant cannot be applied uniformly in the inner surface of the tire.If a scratch is made by the hand of an operator in the step or a user,or for another reason, the light sealing layer does not achieve itsfunction, resulting in degraded durability due to ultravioletdegradation.

Japanese Patent Laying-Open No. 2005-343379 (PTD 8) achieves improvementin low temperature durability by designing the thickness at a shoulderpart larger than the thickness at a tire crown portion. The thickness atthe shoulder part is designed to be thicker than that at the tire crownportion to suppress flection deformation and reduce the occurrence ofcracks, however, it is disadvantageous in view of weight reduction of atire.

CITATION LIST Patent Document

-   PTD 1: Japanese Patent Laying-Open No. 9-019987-   PTD 2: Japanese Patent No. 2999188 (Japanese Patent Laying-Open No.    2000-159936)-   PTD 3: Japanese Patent Laying-Open No. 2008-024219-   PTD 4: Japanese Patent Laying-Open No. 2008-174037-   PTD 5: Japanese Patent Laying-Open No. 2007-291256-   PTD 6: Japanese Patent Laying-Open No. 2009-298986-   PTD 7: WO2007/16983-   PTD 8: Japanese Patent Laying-Open No. 2005-343379

SUMMARY OF INVENTION Technical Problem

A first subject of the present invention is to provide a pneumatic tireincluding an inner liner, in which air permeability resistance, flectionfatigue resistance and crack resistance are improved.

A second subject of the present invention is to provide a pneumatic tireincluding an inner liner, in which detachment strength between the innerliner and a carcass ply is increased, and air permeability resistance,flection fatigue resistance and crack resistance are further improved.

A third subject of the present invention is to provide a pneumatic tireincluding an inner liner, in which flection crack growth resulting fromrepeated flection deformation during traveling with the tire isprevented in the inner liner, and in which weather resistance, airpermeability resistance and rolling resistance are improved as a whole.

Solution to Problem

In relation to the first subject, the present invention relates to apneumatic tire including an inner liner disposed on an inner side of thetire. The inner liner is composed of a sheet made of an elastomercomposition containing an elastomer component in which astyrene-isobutylene-styrene triblock copolymer by more than or equal to7 percent by mass and less than or equal to 93 percent by mass and anisobutylene-based modified copolymer containing a β-pinene component bymore than or equal to 7 percent by mass and less than or equal to 93percent by mass are mixed. In the inner liner, a ratio Gs/Gb between anaverage thickness Gb in a bead region Rb extending from a tire largestwidth position to a bead toe and an average thickness Gs in a buttressregion Rs extending from the tire largest width position to acorresponding position Lu at a belt layer end is 0.30 to 0.75.

Desirably, the styrene-isobutylene-styrene triblock copolymer contains astyrene component at a content of 10 percent by mass to 30 percent bymass, and has a weight average molecular weight of 50,000 to 400,000.Preferably, the isobutylene-based modified copolymer is contained bymore than or equal to 10 percent by mass and less than or equal to 90percent by mass in the elastomer component of the elastomer composition.

Preferably, β-pinene in the isobutylene-based modified copolymer iscontained at a content of 0.5 percent by mass to 25 percent by mass.Preferably, the isobutylene-based modified copolymer has a weightaverage molecular weight Mw of 30,000 to 300,000, and a value of amolecular weight distribution (weight average molecular weight Mw/numberaverage molecular weight Mn) is less than or equal to 1.3.

Preferably, the average thickness Gs in the buttress region of the innerliner is 0.05 mm to 0.45 mm.

In relation to the second subject, the present invention relates to apneumatic tire including an inner liner disposed on an inner side of thetire. The inner liner is composed of a polymer sheet made of anelastomer composition containing a SIBS modified copolymer obtained bymodifying a styrene block portion of a styrene-isobutylene-styrenetriblock copolymer with one of acid chloride and acid anhydride havingan unsaturated bond. In the inner liner, a ratio (Gs/Gb) between anaverage thickness Gb in a bead region Rb extending from a tire largestwidth position to a bead toe and an average thickness Gs in a buttressregion Rs extending from the tire largest width position to acorresponding position Lu at a belt layer end is 0.30 to 0.75.

Desirably, the styrene-isobutylene-styrene triblock copolymer contains astyrene component at a content of 10 percent by mass to 30 percent bymass, and has a weight average molecular weight ranging from 50,000 to400,000. Desirably, the SIBS modified copolymer is contained by morethan or equal to 10 percent by mass and less than or equal to 100percent by mass in an elastomer component.

In the present invention, the elastomer component can be a mixture ofthe styrene-isobutylene-styrene triblock copolymer and the SIBS modifiedcopolymer. Desirably, the elastomer composition has blended therein atackifier by 0.1 part by mass to 100 parts by mass relative to 100 partsby mass of an elastomer component. In the present invention, desirably,the average thickness Gs in the buttress region of the inner liner is0.05 mm to 0.40 mm.

In relation to the third subject, the present invention relates to apneumatic tire having a carcass layer extending from a tread portion tobead portions on both sides thereof, a belt layer on an outer side of acrown portion thereof, and an inner liner disposed on an inner side ofthe carcass layer. The inner liner is composed of a first layer disposedon an inner side of the tire, and a second layer disposed in contactwith a rubber layer of the carcass ply. (A) The first layer is anelastomer composition containing a thermoplastic elastomer, anultraviolet absorber and an antioxidant, the thermoplastic elastomercontaining at least one of a styrene-isobutylene-styrene block copolymerand a SIBS modified copolymer obtained by modifying a styrene blockportion of a styrene-isobutylene-styrene block copolymer with one ofacid chloride and acid anhydride having an unsaturated bond. (B) Thesecond layer contains an elastomer containing at least one of astyrene-isoprene-styrene block copolymer and a styrene-isobutylene blockcopolymer. The first layer and the second layer are elastomercompositions containing the ultraviolet absorber and the antioxidant by0.5 percent by mass to 40 percent by mass in total of an elastomercomponent. In the inner liner, an average thickness Gs in a buttressregion Rs extending from a tire largest width position to acorresponding position Lu at a belt layer end is thinner than an averagethickness Gb in a bead region Rb extending from the tire largest widthposition to a bead toe.

Preferably, a total blending amount of the ultraviolet absorber and theantioxidant in the first and second layers is 0.5 percent by mass to 40percent by mass of the elastomer component.

Preferably, a ratio (Gs/Gb) between the average thickness Gs in thebuttress region and the average thickness Gb in the bead region of theinner liner is 0.5 to 0.7.

Preferably, the average thickness Gs in the buttress region of the innerliner is 0.06 mm to 0.30 mm.

More preferably, the elastomer composition of one of the first layer andthe second layer has blended therein the SIBS modified copolymer by 5percent by mass to 100 percent by mass of the elastomer component.

Preferably, the elastomer composition of one of the first layer and thesecond layer has blended therein one of a tackifier and polyisobutylene.

Advantageous Effects of Invention

A first effect of the present invention is as follows. According to thepresent invention, the inner liner is composed of an elastomercomposition containing a styrene-isobutylene-styrene triblock copolymerand an isobutylene-based modified copolymer containing β-pinene.Therefore, the thickness thereof can be made thin while maintaining airpermeability resistance. Adhesive property with an adjacent rubber layercan also be improved, and flection fatigue resistance is furtherimproved. As for the average thickness of the inner liner composed ofthe above-described elastomer composition, an average thickness (Gb) inbead region Rb is made thicker within a certain range than Gs inbuttress region Rs. Therefore, stress resulting from repeated flectiondeformation during traveling with the tire can be effectively relaxedwhile maintaining air permeability resistance and flection fatigueresistance. Crack resistance is thus improved.

The second effect of the present invention is as follows. According tothe present invention, in order to effectively relax shearing stress inthe buttress portion in which stress concentration resulting fromrepeated flection deformation during traveling with the tire is likelyto occur, the ratio between average thickness Gb in bead region Rb andaverage thickness Gs in buttress region Rs of the inner liner isadjusted, and an elastomer composition containing a modified SIBS isused for the inner liner. Accordingly, a pneumatic tire increased inadhesive property with an adjacent rubber layer and improved in airshutoff property, flection fatigue resistance and crack resistance canbe obtained while maintaining the thickness of the inner liner thin.

The third effect of the present invention is as follows. The presentinvention effectively relaxes stress on the buttress region resultingfrom repeated flection deformation by making the ratio (Gs/Gb) betweenaverage thickness Gs in buttress region Rs and average thickness Gb inbead region Rb of the inner liner smaller than 1. In addition, athermoplastic elastomer composition containing astyrene-isobutylene-styrene block copolymer (SIBS) is used for the innerliner. Here, a composition containing the SIBS and the like is likely tosuffer from degradation in a wavelength range of an ultravioletwavelength of more than or equal to 290 nm. Then, by blending anultraviolet absorber with the thermoplastic elastomer composition, afunction is provided which absorbs light around 320 nm to 350 nm wheredegradation is most likely to occur and convert the light into molecularvibrational energy or thermal energy, thereby protecting thethermoplastic elastomer from ultraviolet light. Here, the ultravioletabsorber also includes a light stabilizer.

Moreover, in the thermoplastic elastomer, a radical is produced due toflection fatigue during traveling with the tire. The radical induceslinked degradation of a main chain, and invites cracks and destructionof the inner liner made of the thermoplastic elastomer composition.Then, blending an antioxidant serves to capture the radical produced byflection fatigue and prevent degradation. Here, the antioxidant alsoincludes an oxygen absorber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross sectional view showing the right half of apneumatic tire according to an embodiment of the present invention.

FIG. 2 is a schematic cross sectional view showing a bonding state of aninner liner and a carcass.

DESCRIPTION OF EMBODIMENTS First Embodiment

<Pneumatic Tire>

The following describes an embodiment of a pneumatic tire of the presentinvention with reference to the drawings. FIG. 1 is a schematic crosssectional view of the right half of a pneumatic tire for a passengercar. Pneumatic tire 1 includes a tread portion 2, and a sidewall portion3 and bead portions 4 so as to form a shape of toroid from the oppositeends of the tread portion. In each of bead portions 4, a bead core 5 isembedded. Further, a carcass ply 6 and a belt layer 7 are disposed.Carcass ply 6 is provided to extend from one bead portion 4 to the otherbead portion, and is anchored by folding its ends around bead cores 5.Belt layer 7, which is formed of at least two plies, is disposed outsidea crown portion of carcass ply 6.

Belt layer 7 is disposed such that two plies, which are formed of steelcords or cords of aramid fibers or the like, are arranged to allow thecords to cross each other between the plies normally at an angle of 5°to 30° relative to the tire circumferential direction. It should benoted that topping rubber layers can be provided on the outer side ofthe opposite ends of the belt layer to reduce detachment in the oppositeends of the belt layer. Further, in the carcass ply, organic fiber cordssuch as polyester, nylon, or aramid are arranged at substantially 90°relative to the tire circumferential direction. In a region surroundedby the carcass ply and its folded portion, a bead apex 8 is disposed toextend from the upper end of bead core 5 in the sidewall direction.Further, an inner liner 9 is disposed on the inner side of carcass ply 6in the tire radial direction, so as to extend from one bead portion 4 tothe other bead portion 4.

In the present invention, an average thickness Gs of inner liner 9 in abuttress region Rs extending from tire largest width position Le to acorresponding position Lu at the end of the belt layer is formed to bethinner than an average thickness Gb of inner liner 9 in a bead regionRb extending from tire largest width position Le to a bead toe Lt.

By making the average thickness (Gs) of the inner liner in buttressregion Rs thinner, even if shearing deformation takes place due torepeated flection deformation in this region during traveling with thetire, resultant stress can be relaxed to prevent cracks from occurring.

In order to effectively relax stress caused by flection deformation, theratio (Gs/Gb) between average thickness Gs in buttress region Rs andaverage thickness Gb in bead region Rb of the inner liner is adjusted tofall within a range of 0.30 to 0.75. In order to attain the effect ofrelaxing stress in the buttress region while maintaining airpermeability resistance, average thickness Gs in buttress region Rs ofthe inner liner is desirably 0.05 mm to 0.45 mm.

<Elastomer Composition>

In the present invention, the inner liner is composed of an elastomercomposition containing an elastomer component in which astyrene-isobutylene-styrene triblock copolymer (hereinafter alsoreferred to as “SIBS”) and an isobutylene-based modified copolymercontaining β-pinene are mixed.

The elastomer composition contains an elastomer component in which astyrene-isobutylene-styrene triblock copolymer by more than or equal to7 percent by mass and less than or equal to 93 percent by mass and anisobutylene-based modified copolymer containing a β-pinene component bymore than or equal to 7 percent by mass and less than or equal to 93percent by mass are mixed. Preferably, the isobutylene-based modifiedcopolymer containing 1-pinene ranges from 10 percent by mass to 90percent by mass of the entire elastomer component. If theisobutylene-based modified copolymer is less than 7 percent by mass,vulcanization adhesion strength with an adjacent carcass ply may bereduced. On the other hand, if the isobutylene-based modified copolymerexceeds 93 percent by mass, air permeability resistance and crackresistance will be degraded.

<SIBS>

Because of the isobutylene block in the SIBS, a film containing the SIBShas excellent air permeability resistance. Therefore, by using this foran inner liner, a pneumatic tire excellent in air permeabilityresistance can be obtained. Moreover, since the molecular structure ofthe SIBS is completely saturated except aromatic side chain, hardeningdegradation is suppressed, and when the SIBS is applied to a tire, thetire has excellent durability. Furthermore, since the SIBS has high airpermeability resistance, it is not necessary to use a halogenatedrubber, such as a halogenated butyl rubber, which has beenconventionally used to provide air permeability resistance and has ahigh specific gravity. Accordingly, weight reduction of the tire can beachieved, thus improving fuel efficiency.

As to the molecular weight of the SIBS, the SIBS preferably has a weightaverage molecular weight of 50,000 to 400,000 measured through GPCmeasurement, in view of flowability, shaping step, rubber elasticity,and the like. When the weight average molecular weight thereof is lessthan 50,000, tensile strength and tensile elongation may be unfavorablydecreased. On the other hand, when the weight average molecular weightthereof exceeds 400,000, extrusion workability may unfavorably becomebad. In order to further improve air permeability resistance anddurability, the SIBS preferably contains the styrene component at acontent of 10 percent by mass to 30 percent by mass, preferably 14percent by mass to 23 percent by mass.

In the copolymer of the SIBS, the isobutylene block preferably has adegree of polymerization in a range of approximately 10,000 to 150,000,and the styrene block preferably has a degree of polymerization in arange of approximately 5,000 to 30,000, in view of rubber elasticity andhandling (when the degree of polymerization is less than 10,000, eachblock will be in a liquid form). The SIBS can be obtained through ageneral living cationic polymerization method for a vinyl-basedcompound.

<Isobutylene-Based Modified Copolymer>

In the present invention, the isobutylene-based modified copolymer is anisobutylene-based modified copolymer made of a polymeric block (A)mainly containing isobutylene and a polymeric block (B) mainlycontaining an aromatic vinyl-based compound, and is a random copolymerin which at least one block contains β-pinene.

The polymeric block (A) containing isobutylene as a main component is apolymeric block containing a unit whose soft segment originates inisobutylene by more than or equal to 80 percent by mass. This polymericblock can be produced using aliphatic olefins, dienes, vinyl ethers,silanes, vinylcarbazole, acenaphthylene, or the like as a monomercomponent.

On the other hand, the polymeric block (B) mainly containing an aromaticvinyl-based compound is a polymeric block containing a unit whose hardsegment originates in the aromatic vinyl-based compound by more than orequal to 80 percent by mass.

Examples of the aromatic vinyl-based compound include styrene,methylstyrene, α-methylstyrene, β-methylstyrene, 2,6-dimethylstyrene,2,4-dimethylstyrene, α-methyl-o-methylstyrene, α-methyl-m-methylstyrene,α-methyl-p-methylstyrene, α-methyl-o-methylstyrene,β-methyl-m-methylstyrene, β-methyl-p-methylstyrene, 2,4,6-trimethylstyrene, α-methyl-2,6-dimethylstyrene, α-methyl-2,4-dimethylstyrene,β-methyl-2,6-dimethylstyrene, O-methyl-2,4-dimethylstyrene,chlorostyrene, 2,6-dichlorostyrene, 2,4-dichlorostyrene,α-chloro-o-chlorostyrene, α-chloro-m-chlorostyrene,α-chloro-p-chlorostyrene, β-chloro-o-chlorostyrene,β-chloro-m-chlorostyrene, β-chloro-p-chlorostyrene,2,4,6-trichlorostyrene, α-chloro-2,6-dichlorostyrene,α-chloro-2,4-dichlorostyrene, β-chloro-2,6-dichlorostyrene,β-chloro-2,4-dichlorostyrene, t-butylstyrene, methoxy styrene,chloromethylstyrene, bromomethylstyrene, and the like. Particularly inview of cost, styrene and α-methylstyrene are preferable.

In the isobutylene-based modified copolymer of the present invention, atleast one block of the polymeric blocks (A) and (B) is a randomcopolymer with β-pinene. in view of low temperature characteristics,copolymerization with the polymeric block (B) mainly containing anaromatic vinyl-based compound is preferable.

On the other hand, in view of adhesive property, copolymerization withthe polymeric block (A) mainly containing isobutylene is preferable. Inthis case, the content of β-pinene is preferably 0.5 percent by mass to25 percent by mass of the isobutylene-based modified copolymer, and morepreferably 2 percent by mass to 25 percent by mass. If the content ofβ-pinene is less than 0.5 percent by mass, adhesive property isinsufficient. If the content of β-pinene exceeds 25 percent by mass, thecopolymer will be fragile, and rubber elasticity is likely to decrease

The constitution of the isobutylene-based modified copolymer of thepresent invention is not particularly limited. Any of a block copolymer,a triblock copolymer, a multi-block copolymer and the like having astraight-chain, branched or star-like molecular chain structure can beselected. In view of property balance and molding workability, as forthe polymeric blocks (A) and (B), the constitution of a diblockcopolymer ((A)-(B)) or a triblock copolymer ((B)-(A)-(B)) can beadopted. They can be used alone independently or two or more of them canbe used in combination to obtain desired physical properties and moldingworkability.

The isobutylene-based modified copolymer preferably has a weight averagemolecular weight of 30,000 to 300,000, particularly preferably 30,000 to150,000 measured through GPC measurement, in view of flowability,shaping workability, rubber elasticity, and the like. If the weightaverage molecular weight is less than 30,000, mechanical physicalproperties are less likely to be fully exhibited. On the other hand, ifthe weight average molecular weight exceeds 300,000, flowability andworkability are likely to degrade. Furthermore, in view of processingstability, the value of a molecular weight distribution of theisobutylene-based modified copolymer (weight average molecularweight/number average molecular weight) is less than or equal to 1.3.

<Method for Producing Isobutylene-Based Modified Copolymer>

A method for producing an isobutylene-based modified copolymer isdisclosed in Japanese Patent Laying-Open No. 2010-195969, for example.For example, the copolymer can be produced by polymerizing theabove-described monomer component in the presence of a polymerizationinitiator expressed by the following general formula (I).

(CR¹R²X)nR³  (1)

(wherein X is a substituent selected from a halogen atom, alkoxy groupsor acyloxy groups having 1 to 6 carbon atoms, each of R¹ and R² is ahydrogen atom or a monovalent hydrocarbon group having 1 to 6 carbonatoms, R¹ and R² may be the same or may be different, R³ is a monovalentor multivalent aromatic hydrocarbon group or a monovalent or multivalentaliphatic hydrocarbon group, and n indicates a natural number of 1 to6).

The compound expressed by the above-mentioned general formula (1) servesas an initiator, and generates carbonium ion in the presence of Lewisacid or the like, and serves as a starting point of cationicpolymerization. Examples of the compound of the above-mentioned generalformula (I) include bis(1-chlor-1-methylethyl)benzene [C₆H₄(C(CH₃)₂Cl)₂]and tris(1-chlor-1-methylethyl) benzene [(ClC(CH₃)₂)₃C₆H₃].

When producing the isobutylene-based modified copolymer, a Lewes acidcatalyst can also coexist further. The Lewis acid can be used forcationic polymerization, and a metal halide such as TiCl₄, TiBr₄, BCl₃,BF₃, BF₃OEt₂, ZnBr₂, or AlCl₃ and an organic metal halide such asEt₂AlCl or EtAlCl₂ can be used, for example. The above-mentioned Lewisacid can be used by 0.1 molar equivalent to 100 molar equivalent withrespect to the compound indicated by the general formula (1).

When producing the isobutylene-based modified copolymer, an electrondonor component can also exist. Examples of this electron donorcomponent include pyridines, amines, amides, and sulfoxides.

Polymerization of the isobutylene-based modified copolymer can beperformed in an organic solvent, and an organic solvent that does notinhibit cationic polymerization can be used here. For example,halogenated hydrocarbons such as methyl chloride, dichloromethane,chloroform, ethyl chloride, and dichloroethane, alkylbenzenes such asbenzene, toluene, xylene, and ethylbenzene, straight aliphatichydrocarbons such as ethane, propane, butane, pentane, hexane, andheptane, branched aliphatic hydrocarbons such as 2-methylpropane and2-methylbutane, cyclic aliphatic hydrocarbons such as cyclohexane,methylcyclohexane, and ethylcyclohexane, and the like can be used.

In view of viscosity adjustment and heat dissipation of a copolymersolution to be generated, the amount of the above-described organicsolvent is adjusted such that the concentration of the copolymer is 5percent by mass to 40 percent by mass. It is noted that thecopolymerization reaction preferably occurs in a range of −20° C. to−70° C.

<Third Elastomer Component>

The elastomer composition of the inner liner in the present inventioncan be blended with another thermoplastic elastomer, particularly, astyrene-based thermoplastic elastomer, in a range less than or equal to30 percent by mass of the elastomer component. Here, the styrene-basedthermoplastic elastomer refers to a copolymer including a styrene blockas a hard segment. Examples thereof include: a styrene-isoprene-styreneblock copolymer (hereinafter, also referred to as “SIS”); astyrene-isobutylene block copolymer (hereinafter, also referred to as“SIB”); a styrene-butadiene-styrene block copolymer (hereinafter, alsoreferred to as “SBS”); a styrene-ethylene butene-styrene block copolymer(hereinafter, also referred to as “SEBS”); a styrene-ethylenepropylene-styrene block copolymer (hereinafter, also referred to as“SEPS”); a styrene-ethylene ethylene propylene-styrene block copolymer(hereinafter, also referred to as “SEEPS”); and a styrene-butadienebutylene-styrene block copolymer (hereinafter, also referred to as“SBBS”).

Further, the styrene-based thermoplastic elastomer may have an epoxygroup in its molecular structure. A usable example thereof is EpofriendA1020 provided by Daicel Chemical Industries Ltd., i.e., an epoxymodified styrene-butadiene-styrene copolymer (epoxidized SBS) (having aweight average molecular weight of 100,000 and an epoxy equivalent of500).

It is noted that the thickness of the inner liner of the presentinvention differs between the bead region and the buttress region asdescribed above, but is desirably adjusted in a range of 0.05 mm to 2.0mm. If the thickness is less than 0.05 mm, the inner liner may be brokenby pressing pressure when vulcanizing the raw tire, with the result thatan air leakage phenomenon may take place in the vulcanized tire. On theother hand, if the thickness of the inner liner exceeds 2.0 mm, theweight of the tire is increased to result in disadvantageous performancein fuel efficiency. For the inner liner, a general method for formingthermoplastic elastomer into a film, such as extrusion molding orcalender molding, can be used.

Second Embodiment

<Pneumatic Tire>

In the present embodiment, the structure of a pneumatic tire can besimilar to that of the first embodiment.

<Polymer Sheet>

(SIBS Modified Copolymer)

In the present invention, a polymer sheet used for the inner liner is athermoplastic elastomer composition containing a SIBS modified copolymerobtained by modifying a styrene block portion of astyrene-isobutylene-styrene block copolymer (hereinafter also referredto as “SIBS”) with acid chloride or acid anhydride having an unsaturatedbond.

The above-described polymer sheet preferably contains a SIBS modifiedcopolymer by 10 percent by mass to 100 percent by mass of an elastomercomponent. Here, the SIBS modified copolymer has its styrene blockportion modified with acid chloride or acid anhydride having anunsaturated bond, and contains a chemical constitution of the followingformula (1) in the molecular chain.

In Formula (1), R₁ is a monovalent organic group having a functionalgroup.

Examples of acid chloride having an unsaturated bond used formodification in the present invention include methacrylic acid chloride,methacrylic acid bromide, methacrylic acid iodide, acrylic acidchloride, acrylic acid bromide, acrylic acid iodide, crotonic acidchloride, and crotonic acid bromide. In particular, methacrylic acidchloride and acrylic acid chloride are suitable.

Examples of acid anhydride include acetic anhydride, maleic anhydride,phthalic anhydride, and the like. Acetic anhydride is particularlysuitable. Two or more of these compounds can also be used incombination. Through such modification, the unsaturated group isintroduced into the SIBS, which enables crosslinking through use of across linking agent.

As described above, the blending amount of the SIBS modified copolymerranges from 10 percent by mass to 100 percent by mass, preferably 30percent by mass to 100 percent by mass of the elastomer component. Ifthe blending amount of the SIBS modified copolymer is less than 10percent by mass of the elastomer component, vulcanization adhesionbetween the inner liner and the carcass ply rubber may be insufficient.

The SIBS modified copolymer contains acid chloride and acid anhydridehaving an unsaturated bond at a content of more than or equal to 1percent by weight, preferably more than or equal to 5 percent by weight,and less than or equal to 30 percent by weight. In order to crosslinkthe SIBS modified copolymer, a conventional method can be used. Forexample, thermal crosslinking by heating or crosslinking by a crosslinking agent can be performed. As the cross linking agent, organicperoxide, such as, for example, dicumylperoxide, di-tert-butyl peroxide,2,5-dimethyl-2,5-di-(tert-butylperoxy) hexane, or the like can be used.The blending amount of organic peroxide preferably ranges from 0.1 partby mass to 3.0 parts by mass relative to 100 parts by mass of thethermoplastic elastomer component.

In the elastomer composition of the polymer sheet of the presentinvention, polyfunctional vinyl monomer such as divinylbenzene ortriaryl cyanurate, or a polyfunctional methacrylate monomer such asethylene glycol dimethacrylate, diethylene glycol dimethacrylate,triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate,trimethylolpropane trimetacrylate, or allyl methacrylate can be used incombination as a cross linking agent. In this case, the compositionafter crosslinking can be expected to have improved flection crackcharacteristics.

Because of the isobutylene block in the SIBS modified copolymer, a filmmade of the SIBS modified copolymer has excellent air permeabilityresistance. Moreover, since the unsaturated group is introduced into theSIBS, the SIBS modified copolymer enables thermal crosslinking andcrosslinking by a cross linking agent. Thus, flection crackcharacteristics and air permeability resistance are improved togetherwith basic characteristics such as tensile strength, break elongationand permanent strain. The characteristics as the inner liner are thusimproved.

When manufacturing a pneumatic tire by applying a polymer film made ofan elastomer composition containing the SIBS modified copolymer to theinner liner, air permeability resistance can be secured. Therefore, itis not necessary to use a halogenated rubber, such as a halogenatedbutyl rubber, which has been conventionally used to provide airpermeability resistance and has a high specific gravity. Even if it isused, an amount of usage thereof can be reduced. Accordingly, weightreduction of the tire can be achieved, thus obtaining the effect ofimproving fuel efficiency.

The molecular weight of the SIBS modified copolymer is not particularlylimited, but the SIBS modified copolymer preferably has a weight averagemolecular weight of 50,000 to 400,000 measured through GPC measurement,in view of flowability, shaping step, rubber elasticity, and the like.When the weight average molecular weight thereof is less than 50,000,tensile strength and tensile elongation may be unfavorably decreased. Onthe other hand, when the weight average molecular weight thereof exceeds400,000, extrusion workability may unfavorably become bad. In order tofurther improve air permeability resistance and durability, the SIBSmodified copolymer preferably contains the styrene component at acontent of 10 percent by mass to 30 percent by mass, preferably 14percent by mass to 23 percent by mass.

(Production of SIBS Modified Copolymer)

The SIBS can be obtained through a general living cationicpolymerization method for a vinyl-based compound. For example, each ofJapanese Patent Laying-Open No. 62-48704 and Japanese Patent Laying-OpenNo. 64-62308 discloses that living cationic polymerization betweenisobutylene and another vinyl compound is possible and use ofisobutylene and another compound for a vinyl compound allows forproduction of a polyisobutylene-based block copolymer.

For producing the SIBS modified copolymer, the following method can beadopted, for example. A styrene-isobutylene-styrene block copolymer isinput into a separable flask, and then the atmosphere in apolymerization container is substituted by nitrogen. Then, an organicsolvent (e.g., n-hexane and butyl chloride) having been dried withmolecular sieves is added, and methacrylic acid chloride is furtheradded. At last, aluminum trichloride is added while stirring thesolution to produce a reaction. A predetermined amount of water is addedto the reaction solution after a certain period of time since the startof reaction, and the solution is stirred. The reaction is thenterminated. The reaction solution is washed several times or more with alarge amount of water, and further, slowly dropped into a large amountof a methanol-acetone mixed solvent to precipitate a polymer. Theresulting polymer is vacuum dried. It is noted that the method ofproducing the SIBS modified copolymer is disclosed in Japanese PatentNo. 4551005, for example.

(Thermoplastic Elastomer Composition Containing SIBS Modified Copolymer)

The above-described polymer composition is an elastomer compositioncontaining the SIBS modified copolymer. That is, the SIBS modifiedcopolymer is preferably contained in the elastomer component by morethan or equal to 10 percent by mass, and further, more than or equal to35 percent by mass. Here, although a styrene-based thermoplasticelastomer, an urethane-based thermoplastic elastomer or the like can besuitably used for the elastomer component, SIBS, SIS or SIB isparticularly preferable.

In the present invention, a rubber component can be blended into theelastomer composition. By blending the rubber component, tackiness withan adjacent carcass ply in an unvulcanized state can be provided, andvulcanization adhesive property with the carcass ply or the insulationcan be increased through vulcanization. As the rubber component, atleast one selected from the group consisting of a natural rubber, anisoprene rubber, a chloroprene rubber, and a butyl rubber is preferablycontained. The blending amount of the rubber component preferably rangesfrom 5 percent by mass to 75 percent by mass in the polymer component.

(Tackifier)

In the present invention, a tackifier can be blended into the elastomercomposition for an inner liner in a range of 0.1 part by mass to 100parts by mass with respect to 100 parts by mass of the elastomercomponent. Here, the tackifier refers to a compounding agent forincreasing tackiness of the elastomer composition. Examples of such atackifier will be illustrated below.

Typically, there are C9 petroleum resin and C5 petroleum resin. Here, aC9 petroleum resin is an aromatic petroleum resin obtained bypolymerizing C5 to C9 fractions (mainly C9 fraction) in a mixed state.The C5 to C9 fractions are remnants when obtaining useful compounds,such as ethylene, propylene, and butadiene, by thermally decomposingnaphtha. Examples thereof include products such as: ARKON P70, P90,P100, P125, P140, M90, M100, M115, and M135 (each provided by ArakawaChemical Industries, Ltd., and having a softening point of 70° C. to145° C.); I-MARV S100, SI 10, P100, P125, and P140 (aromaticcopolymer-based hydrogenated petroleum resins each provided by IdemitsuPetrochemical Ltd., and having a softening point of 100° C. to 140° C.,a weight average molecular weight of 700 to 900, and a bromine number of2.0 g/100 g to 6.0 g/100 g); and Petcoal XL (provided by TOSOHCorporation).

A C5 petroleum resin is an aliphatic petroleum resin obtained bypolymerizing C4 to C5 fractions (mainly C5 fraction) in a mixed state.The C4 to C5 fractions are remnants when obtaining useful compounds,such as ethylene, propylene, and butadiene, by thermally decomposingnaphtha. Examples thereof include products such as: Hilets G100(provided by Mitsui Petrochemicals Industries, Ltd., and having asoftening point of 100° C.); Marcalets T100AS (provided by MaruzenPetrochemical Co., Ltd., and having a softening point of 100° C.); andEscorez 1102 (provided by Tonex Co., Ltd., and having a softening pointof 110° C.).

Examples of the terpene resin include products such as: YS resin PX800N,PX000, PX1150, PX1250, and PXN1150N; and Clearon P85, P105, P115, P125,P135, P150, M105, M115, and K100 (each provided by Yasuhara ChemicalCo., Ltd., and having a softening point of 75° C. to 160° C.).

Examples of the aromatic modified terpene resin include products suchas: YS resin TO85, TO105, TO115, and TO125 (each provided by YasuharaChemical Co., Ltd., and having a softening point of 75° C. to 165° C.).

Examples of the terpene phenol resin include products such as: Tamanol803L, 901 (provided by Arakawa Chemical industries Co., Ltd., and havinga softening point of 120° C. to 160° C.); and YS Polyster U115, U130,T80, T100, T115, T145, and T160 (each provided by Yasuhara Chemical Co.,Ltd., and having a softening point of 75° C. to 165° C.).

Examples of the cumarone resin include a cumarone resin having asoftening point of 90° C. (provided by Kobe Oil Chemical Industrial Co.,Ltd.). Examples of the cumarone indene oil include products such as 15SE(provided by Kobe Oil Chemical Industrial Co., Ltd., and having a pourpoint of 15° C.).

Examples of the rosin ester include products such as: ester gum AAL, A,AAV, 105, AT, H, HP, and HD (each provided by Arakawa ChemicalIndustries Co., Ltd., and having a softening point of 68° C. to 110°C.); and Hariester TF, S, C, DS70L, DS90, and DS130 (each provided byHarima Chemicals Inc., and having a softening point of 68° C. to 138°C.). Examples of the hydrogenated rosin ester include products such asSuperester A75, A100, A115, and A125 (each provided by Arakawa ChemicalIndustries Co., Ltd., and having a softening point of 70° C. to 130°C.).

Examples of the alkylphenol resin include products such as Tamanol 510(provided by Arakawa Chemical Industries Co., Ltd., and having asoftening point of 75° C. to 95° C.). Examples of the DCPD includeproducts such as Escorez 5300 (provided by Tonex Co., Ltd., and having asoftening point of 105° C.).

For the tackifier, a fully hydrogenated petroleum resin of the C9petroleum resins is well compatible with the SIB, and can improveadhesive property without decreasing the gas barrier property. Further,it has an effect of decreasing viscosity, and therefore can be usedadvantageously for film extrusion molding.

The tackifier is blended in a range of 0.1 part by mass to 100 parts bymass, preferably, 1 part by mass to 50 parts by mass relative to 100parts by mass of the elastomer component. If the tackifier is blended byless than 0.1 part by mass, vulcanization adhesion strength with thecarcass ply will be insufficient. On the other hand, if the tackifier isblended by more than 100 parts by mass, the tackiness will become toohigh, with the result that workability and productivity are decreasedand the gas barrier property is also decreased.

A second layer can further be stacked on the polymer sheet used for theinner liner of the present invention to obtain a composite layer. Forthe polymer sheet, a general method for forming thermoplastic resin orthermoplastic elastomer into a film, such as extrusion molding orcalender molding, can be adopted. It is noted that the thickness of theinner liner is desirably adjusted to fall within a range of 0.05 mm to0.6 mm.

<Method for Manufacturing Pneumatic Tire>

For the pneumatic tire of the present invention, a general manufacturingmethod can be used. The pneumatic tire can be manufactured by applyingthe polymer sheet to the inner liner of a raw tire and molding themthrough vulcanization together with other members. When disposing thepolymer sheet in the raw tire, the polymer sheet is arranged toward theouter side in the tire radial direction so as to be in contact with acarcass ply. With such arrangement, adhesive strength between thepolymer sheet and the carcass ply can be increased in the step ofvulcanizing the tire. In the resulting pneumatic tire, the inner linerand the rubber layer of the carcass ply are adhered to each other in anexcellent manner. Thus, the pneumatic tire can have excellent airpermeability resistance and durability. It is noted that, since thepolymer sheet containing the SIBS modified copolymer is in a softenedand fluid state in the vulcanization step, problems may arise indeformation or sticking to an adjacent member after vulcanization.Therefore, it is desirable to cool the atmosphere in the bladder aftervulcanization for 10 seconds to 300 seconds to quench the bladder at 50°C. to 120° C.

It should be noted that in order to adjust the thickness of the innerliner in bead region Rb and buttress region Rs, a profile is provided atan extrusion opening for the polymer sheet, whereby a sheet in whichthickness Gs in the buttress region is made thin is obtained in onepiece, and this is disposed on the tire inner surface as the innerliner, for example.

The blending of the rubber layer of the carcass ply used for thepneumatic tire of the present invention can be such that a generallyused rubber component, such as a natural rubber, polyisoprene, astyrene-butadiene rubber, or a polybutadiene rubber, is blended with afiller such as carbon black or silica.

Third Embodiment

<Pneumatic Tire>

In the present embodiment, the structure of a pneumatic tire can besimilar to that of the first embodiment.

In order to effectively relax stress caused by flection deformation, theratio (Gs/Gb) between average thickness Gs in buttress region Rs andaverage thickness Gb in bead region Rb of the above-described innerliner is less than 1, preferably 0.5 to 0.7. In order to attain both theeffects of maintaining the air pressure retaining performance andrelaxing stress in the buttress region, average thickness Gs in buttressregion Rs of the above-described inner liner is desirably 0.05 mm to0.40 mm.

<Inner Liner>

The present invention provides a pneumatic tire including an inner linerdisposed on the inner side of the tire, wherein the inner liner isformed of a polymer layer stack of at least two layers. A first layer isan elastomer composition containing a styrene-isobutylene-styrenetriblock copolymer (SIBS) as a main component, and a second layer is anelastomer composition containing at least one of astyrene-isoprene-styrene triblock copolymer (SIS) and astyrene-isobutylene diblock copolymer (SIB) as a main component.

As the elastomer components of the first layer and the second layer, astyrene-isobutylene-styrene block copolymer (hereinafter also referredto as a “SIBS modified copolymer”) obtained by modifying a styrene blockportion of the SIBS with acid chloride or acid anhydride having anunsaturated bond can be contained. The elastomer compositions of thefirst layer and the second layer contain an ultraviolet absorber and anantioxidant.

<Elastomer Component of First Layer>

In the present invention, the first layer contains astyrene-isobutylene-styrene block copolymer (hereinafter also referredto as “SIBS”) as an elastomer component. Since the SIBS contains anisobutylene block in the molecular chain, a polymer film thereof hasexcellent air permeability resistance. Therefore, when the SIBS is usedfor the inner liner, a pneumatic tire excellent in air permeabilityresistance can be obtained. Furthermore, since the molecular structureof the SIBS is saturated except the aromatic unit, oxidation degradationis suppressed.

As to the molecular weight of the SIBS, the SIBS preferably has a weightaverage molecular weight of 50,000 to 400,000 measured through GPCmeasurement, in view of flowability, shaping step, rubber elasticity,and the like. When the weight average molecular weight thereof is lessthan 50,000, tensile strength and tensile elongation may be decreased.On the other hand, when the weight average molecular weight thereofexceeds 400,000, extrusion workability may become bad. In order tofurther improve air permeability resistance and durability, the SIBSpreferably contains the styrene component at a content of 10 percent bymass to 30 percent by mass.

In each block in the molecular chain of the SIBS, the isobutylene unitpreferably has a degree of polymerization of approximately 10,000 to150,000, and the styrene unit preferably has a degree of polymerizationof approximately 5,000 to 30,000. The SIBS can be produced through ageneral living cationic polymerization method for a vinyl-basedcompound. For example, each of Japanese Patent Laying-Open No. 62-48704and Japanese Patent Laying-Open No. 64-62308 discloses living cationicpolymerization of isobutylene and another vinyl compound.

<Elastomer Component of Second Layer>

The second layer is an elastomer composition containing at least one ofa styrene-isoprene-styrene block copolymer (hereinafter, also referredto as “SIS”) and a styrene-isobutylene block copolymer (hereinafter,also referred to as “SIB”).

The isoprene block of the styrene-isoprene-styrene copolymer (SIS) is asoft segment. Hence, a polymer film made of the SIS is likely to adhereto a rubber component through vulcanization. Therefore, when the polymerfilm made of the SIS is used for the inner liner, a pneumatic tireexcellent in durability can be obtained because that inner liner isexcellent in adhesive property with the rubber layer of the carcass ply,for example.

The molecular weight of the SIS is not particularly limited, but the SISpreferably has a weight average molecular weight of 100,000 to 290,000measured through GPC measurement, in view of rubber elasticity andmoldability. When the weight average molecular weight thereof is lessthan 100,000, tensile strength may be unfavorably decreased. On theother hand, when the weight average molecular weight thereof exceeds290,000, extrusion workability unfavorably becomes bad. The SISpreferably contains the styrene component at a content of 10 percent bymass to 30 percent by mass in view of tackiness, adhesive property, andrubber elasticity.

In the present invention, it is preferable that in the SIS, the isopreneblock has a degree of polymerization of approximately 500 to 5,000 andthe styrene lock has a degree of polymerization of approximately 50 to1,500 in view of rubber elasticity and handling.

The SIS can be obtained through a general polymerization method for avinyl-based compound, such as the living cationic polymerization method.The SIS layer can be obtained by forming the SIS into the form of a filmby means of a general method for forming thermoplastic resin orthermoplastic elastomer into a film, such as extrusion molding orcalender molding.

The isobutylene block of the styrene-isobutylene block copolymer (SIB)is a soft segment. Hence, a polymer film made of the SIB is likely toadhere to a rubber component through vulcanization. Therefore, when apolymer film made of the SIB is used for the inner liner, a pneumatictire excellent in durability can be obtained because that inner liner isexcellent in adhesive property with an adjacent rubber forming thecarcass or the insulation, for example.

For the SIB, a linear SIB is preferably used in view of rubberelasticity and adhesive property. The molecular weight of the SIB is notparticularly limited, but the SIB preferably has a weight averagemolecular weight of 40,000 to 120,000 measured through GPC measurement,in view of rubber elasticity and moldability. When the weight averagemolecular weight thereof is less than 40,000, tensile strength may beunfavorably decreased. On the other hand, when the weight averagemolecular weight thereof exceeds 120,000, extrusion workability mayunfavorably become bad. The SIB preferably contains the styrenecomponent at a content of 10 percent by mass to 35 percent by mass, inview of tackiness, adhesive property, and rubber elasticity. In thepresent invention, it is preferable that in the SIB, the isobutyleneblock has a degree of polymerization of approximately 300 to 3,000 andthe styrene block has a degree of polymerization of approximately 10 to1,500 in view of rubber elasticity and handling.

The SIB can be obtained through a general living polymerization methodfor a vinyl-based compound. For example, the SIB can be obtained byadding methylcyclohexane, n-butyl chloride, and cumyl chloride into anagitator, cooling them to −70° C., reacting them for 2 hours, thenadding a large amount of methanol to stop the reaction, and performingvacuum-drying at 60° C.

(Mixture with SIBS)

The second layer can be composed of a mixture of the SIS and the SIBS ora mixture of the SIB and the SIBS. In this case, the mixing amount ofthe SIBS is adjusted to fall within a range of 10 percent by mass to 80percent by mass of the thermoplastic elastomer component. If the SIBS isless than 10 percent by mass, adhesive property with the first layer islikely to be decreased. If the SIBS exceeds 80 percent by mass, adhesiveproperty with the carcass ply is likely to be decreased.

<Elastomer Component of First Layer and Second Layer>

(SIBS Modified Copolymer)

The elastomer composition of the first layer can contain the SIBSmodified copolymer by 10 percent by mass to 100 percent by mass of theelastomer component. The elastomer composition of the second layer cancontain the SIBS modified copolymer by 5 percent by mass to 80 percentby mass, preferably 10 percent by mass to 80 percent by mass of theelastomer component. If the SIBS modified copolymer is less than 5percent by mass, vulcanization adhesion strength between the first layerand the second layer or between the second layer and the carcass ply maybe decreased. If the SIBS modified copolymer exceeds 80 percent by mass,adhesion strength with the carcass ply may be decreased.

Here, the SIBS modified copolymer is obtained by modifying the styreneblock moiety of the styrene-isobutylene-styrene block copolymer (SIBS)with acid chloride or acid anhydride having an unsaturated bond, andcontains a chemical constitution expressed by Formula (1) below in themolecular chain.

In Formula (1), n is an integer, and R1 is a monovalent organic grouphaving a functional group.

Examples of acid chloride having an unsaturated bond used formodification in the present invention include methacrylic acid chloride,methacrylic acid bromide, methacrylic acid iodide, acrylic acidchloride, acrylic acid bromide, acrylic acid iodide, crotonic acidchloride, and crotonic acid bromide. In particular, methacrylic acidchloride and acrylic acid chloride are suitable. Examples of acidanhydride include acetic anhydride, maleic anhydride, and phthalicanhydride. Acetic anhydride is particularly suitable. Through suchmodification, the unsaturated group is introduced into the SIBS, whichenables crosslinking of the molecular chain by a cross linking agent.

As described above, the blending amount of the SIBS modified copolymerobtained by modifying the styrene-isobutylene-styrene block copolymerwith acid chloride and acid anhydride having an unsaturated bond rangesfrom 10 percent by mass to 100 percent by mass, preferably 30 percent bymass to 100 percent by mass of a thermoplastic elastomer component. Ifthe blending amount of the SIBS modified copolymer is less than 10percent by mass of the thermoplastic elastomer component, vulcanizationadhesion between the second layer and the carcass ply rubber may beinsufficient.

The SIBS modified copolymer contains acid chloride and acid anhydridehaving an unsaturated bond at a content of more than or equal to 1percent by weight, preferably more than or equal to 5 percent by weight,and less than or equal to 30 percent by weight.

It is noted that, for the SIBS modified copolymer, thermal crosslinkingor crosslinking by a cross linking agent can be performed by aconventional method.

Because of the isobutylene block in the SIBS modified copolymer, a filmmade of the SIBS modified copolymer has excellent air permeabilityresistance. Moreover, in the SIBS modified copolymer, the unsaturatedgroup is introduced into the SIBS. Thus, thermal crosslinking andcrosslinking by a cross linking agent are made possible, and flectioncrack characteristics and air permeability resistance are improvedtogether with basic characteristics such as tensile strength, breakelongation and permanent strain. The characteristics as the inner linerare thus improved.

The molecular weight of the SIBS modified copolymer is not particularlylimited, but the SIBS modified copolymer preferably has a weight averagemolecular weight of 50,000 to 400,000 measured through GPC measurement,in view of flowability, shaping step, rubber elasticity, and the like.If the weight average molecular weight thereof is less than 50,000,tensile strength and tensile elongation may be unfavorably decreased. Onthe other hand, if the weight average molecular weight thereof exceeds400,000, extrusion workability may unfavorably become bad. In order tofurther improve air permeability resistance and durability, the SIBSmodified copolymer preferably contains the styrene component at acontent of 10 percent by mass to 30 percent by mass, preferably 14percent by mass to 23 percent by mass.

In the copolymer of the SIBS, the isobutylene block preferably has adegree of polymerization of approximately 10,000 to 150,000, and thestyrene block preferably has a degree of polymerization of approximately5,000 to 30,000, in view of rubber elasticity and handling (when thedegree of polymerization is less than 10,000, each block will be in aliquid form).

As a method for producing the SIBS modified copolymer, the followingmethod can be adopted, for example. The styrene-isobutylene-styreneblock copolymer is input into a separable flask, and then the atmospherein a polymerization container is substituted by nitrogen. Then, anorganic solvent (e.g., n-hexane and butyl chloride) having been driedwith molecular sieves is added, and methacrylic acid chloride is furtheradded. At last, aluminum trichloride is added while stirring thesolution to produce a reaction. A predetermined amount of water is addedto the reaction solution after a certain period of time since the startof reaction, and the solution is stirred. The reaction is thenterminated. The reaction solution is washed several times or more with alarge amount of water, and further, slowly dropped into a large amountof a methanol-acetone mixed solvent to precipitate a polymer. Theresulting polymer is vacuum dried. It is noted that the method ofproducing the SIBS modified copolymer is disclosed in Japanese PatentNo. 4551005, for example.

(Styrene-Based Thermoplastic Elastomer)

The first layer and the second layer can each contain a styrene-basedthermoplastic elastomer. Here, the styrene-based thermoplastic elastomerrefers to a copolymer including a styrene block as a hard segment. Inaddition to the above-described SIBS, SIS and SIB, examples thereofinclude: a styrene-butadiene-styrene block copolymer (“SBS”); astyrene-isobutylene-styrene block copolymer (“SIBS”); a styrene-ethylenebutene-styrene block copolymer (“SEBS”); a styrene-ethylenepropylene-styrene block copolymer (“SEPS”); a styrene-ethylene ethylenepropylene-styrene block copolymer (“SEEPS”); and a styrene-butadienebutylene-styrene block copolymer (“SBBS”).

Further, the styrene-based thermoplastic elastomer may have an epoxygroup in its molecular structure. A usable example thereof is EpofriendA1020 provided by Daicel Chemical Industries Ltd., i.e., an epoxymodified styrene-butadiene-styrene copolymer (epoxidized SBS) (having aweight average molecular weight of 100,000 and an epoxy equivalent of500).

(Rubber Component)

A rubber component can be blended into the thermoplastic elastomercomposition of the first layer. By blending the rubber component,tackiness with an adjacent carcass ply in an unvulcanized state can beprovided, and vulcanization adhesive property with the carcass ply orthe insulation can be increased through vulcanization.

As the rubber component, at least one selected from the group consistingof a natural rubber, an isoprene rubber, a chloroprene rubber, and abutyl rubber is preferably contained. The blending amount of the rubbercomponent preferably ranges from 5 percent by mass to 75 percent by massof the elastomer component.

<Ultraviolet Absorber>

In the present invention, an ultraviolet absorber is blended into theelastomer composition. The ultraviolet absorber absorbs light in anultraviolet range of wavelength of more than or equal to 290 nm toprevent degradation of the molecular chain of the polymer compound. Forexample, benzophenone-based, salicylate-based, and benzotriazol-basedultraviolet absorbers absorb ultraviolet light of wavelength around 320nm to 350 nm where a polymer compound is most likely to suffer fromdegradation. The absorbers have the function of converting light in thiswavelength range into vibrational energy or thermal energy, therebypreventing such light to be absorbed into the polymer compound. Inparticular, the benzotriazol-based ultraviolet absorber can absorb awide range of ultraviolet light. Here, examples of the ultravioletabsorber are listed below.

[Benzotriazol-Based Ultraviolet Absorber]

TINUVIN P/FL (provided by BASF, and having a molecular weight of 225, amelting point of 128° C. to 132° C., and a maximum absorption wavelengthof 341 nm) (2-(2-hydroxy-benzotriazol-2-yl)-p-cresol), TINUVIN 234(provided by BASF, and having a molecular weight of 447.6, a meltingpoint of 137° C. to 141° C., and a maximum absorption wavelength of 343nm) (2-[2-hydroxy-3,5-bis(α, α′ dimethylbenzyl)phenyl]-2H-benzotriazol), TINUVIN 326/FL (provided by BASF, and having amolecular weight of 315.8, a melting point of 138° C. to 141° C., and amaximum absorption wavelength of 353 nm), ADK STAB LA-36 (provided byADEKA Corporation)(2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazol),TINUVIN 237 (provided by BASF, and having a molecular weight of 338.4, amelting point of 139° C. to 144° C., and a maximum absorption wavelengthof 359 nm) (2,4-di-t-butyl-6-(5-chlorobenzotriazol-2-yl-)phenol),TINUVIN 328 (provided by BASF, and having a molecular weight of 351.5, amelting point of 80° C. to 88° C., and a maximum absorption wavelengthof 347 nm) (2-(3,5-di-t-amyl-2-hydroxyphenyl) benzotriazol), and TINUVIN329/FL (provided by BASF, and having a molecular weight of 323, amelting point of 103° C. to 105° C., and a maximum absorption wavelengthof 343 nm) (2-(2-hydroxy-benzotriazol-2-yl)-4-tert-octylphenol).

[Liquid Ultraviolet Absorber]

TINUVIN 213 (provided by BASF, and having a melting point of −40° C. anda maximum absorption wavelength of 344 nm)(5-(2-hydroxy-benzotriazol-2-yl)-4-hydroxy-3-tert-butylbenzenpropanoicacid methyl), TINUVIN 571 (provided by BASF, and having a molecularweight of 393.6, a melting point of −56° C. and a maximum absorptionwavelength of 343 nm)(2-(2-hydroxybenzotriazol-2-yl)-4-methyl-6-dodecylphenol).

[Triazine-Based Ultraviolet Absorber]

TINUVIN 1577FF (provided by BASF, and having a molecular weight of 425,a melting point of 148° C. and a maximum absorption wavelength of 274nm) (2-[4,6-diphenyl-1,3,5-triazine-2-yl]-5-(hexyloxy)phenol).

[Benzophenone-Based Ultraviolet Absorber]

CHIMASSORB 81/FL (provided by BASF, and having a molecular weight of326.4 and a melting point of 48° C. to 49° C.)(2-hydroxy-4-(octyloxy)benzophenone).

[Benzoate-Based Ultraviolet Absorber]

TINUVIN 120 (provided by BASF, and having a molecular weight of 438.7, amelting point of 192° C. to 197° C., and a maximum absorption wavelengthof 265 nm)(2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate).

[Hindered Amine Stabilizer]

CHIMASSORB 2020 FDL (provided by BASF, and having a molecular weight of2600 to 3400 and a melting point of 130° C. to 136° C.) (polycondensateof dibutylamine 1,3,5-triazineN,N-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamineN-(2,2,6,6-tetramethyl-4-piperidyl)butylamine), CHIMASSORB 944 FDL(provided by BASF, and having a molecular weight of 2000 to 3100 and amelting point of 100° C. to 135° C.) (poly[(6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl){(2,2,6,6-tetramethyl-4-piperidyl)imino} hexamethylene(2,2,6,6-tetramethyl-4-piperidyl)imino)]), TINUVIN 622 LD (provided byBASF, and having a molecular weight of 3100 to 4000 and a melting pointof 55° C. to 70° C.) (butanedioic acid1-[2-(4-hydroxy-2,2,6,6-tetramethyl-piperidino)ethyl]), TINUVIN 144(provided by BASF, and having a molecular weight of 685 and a meltingpoint of 146° C. to 150° C.)(2-butyl-2-[3,5-di(tert-butyl)-4-hydroxybenzyl] malonic acidbis(1,2,2,6,6-pentamethyl-4-piperidyl), TINUVIN 292 (provided by BASF,and having a molecular weight of 509) (sebacic acidbis(1,2,2,6,6-pentamethyl-4-piperidinyl), and TINUVIN 770 DF (providedby BASF, and having a molecular weight of 481 and a melting point of 81°C. to 85° C.) (sebacic acid bis(2,2,6,6-tetramethylpiperidine-4-yl).

<Examples of the Antioxidant are >

In the present invention, an antioxidant is blended into the elastomercomposition. The antioxidant can function as a radical supplementaryagent to mainly supplement a carbon radical, thereby preventingdegradation of the molecular chain of a polymer. Examples of theantioxidant are listed below.

[Hindered Phenolic Antioxidant]

IRGANOX1010 (provided by BASF), ADK STAB AO-60 (provided by ADEKACorporation), SUMILIZER BP-101 (provided by Sumitomo Chemical Co., Ltd.)(pentaerythrityl tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]), IRGANOX1035 (provided by BASF) (2,2-thio-diethylenebis[(3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate)]), IRGANOX1076(provided by BASF) (octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), IRGANOX1098 (provided by BASF)(N,N′-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide),IRGANOX1135 (provided by BASF)(isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]), IRGANOX1330(provided by BASF)(1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene),IRGANOX1726 (provided by BASF) (4,6-bis(dodecylthiomethyl)-O-cresol),IRGANOX1425 (provided by BASF)(bis(3,5-di-t-butyl-4-hydroxybenzylphosphonic acid ethyl) calcium (50%),polyethylene wax (50%)), IRGANOX1520 (provided by BASF) (2,4-bis[(octylthio)methyl]-O-cresol), IRGANOX245 (provided by BASF)(triethyleneglycol-bis[(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate)]), IRGANOX259 (provided by BASF)(1,6-hexanediol-bis[(3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]),IRGANOX3114 (provided by BASF)(tris-(3,5-di-t-butyl-4-hydroxybenzyl)-isocyanurate), IRGANOX5057(provided by BASF) (octylated diphenylamine), IRGANOX565 (provided byBASF)(2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine),Cyanox CY 1790 (provided by Sun Chemical Company Ltd.)(1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid),ADK STAB AO-40 (provided by ADEKA Corporation), SUMILIZER BBM (providedby Sumitomo Chemical Co., Ltd.)(4,4′-butylidenebis(3-methyl-6-t-butylphenol), ADK STAB AO-50 (providedby ADEKA Corporation), SUMILIZER BP-76 (provided by Sumitomo ChemicalCo., Ltd.) (stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl) propionate), ADKSTAB AO-80 (provided by ADEKA Corporation), and SUMILIZER GA-80(provided by Sumitomo Chemical Co., Ltd.) (3,9-bis[,1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy]ethyl] 2,4,8,10-tetraoxaspiro [5,5]-undecane).

[Phosphorus-Based Antioxidant]

A phosphorus-based antioxidant is used as a peroxide decompositionagent, and has an excellent antioxidant function in thermal processingmolding. Examples thereof are listed below.

IRGAFOS12 (provided by BASF, and having a molecular weight of 1462.9)(6,6′,6″-[nitrilotris (ethyleneoxy)] tris(2,4,8,10-tetra-tert-butylbenzo[d, f] [1, 3, 2]dioxaphosphepin)), IRGAFOS38 (provided by BASF, andhaving a molecular weight of 514) (phosphorous acid ethylbis(2,4-di-tert-butyl-6-methylphenyl)), IRGAFOS168 (provided by BASF, andhaving a molecular weight of 646), ADK STAB 2112 (provided by ADEKACorporation), SUMILIZER P-16 (provided by Sumitomo Chemical Co., Ltd.)(tris(2,4-di-t-butylphenyl) phosphite), ADK STAB PEP-8 (provided byADEKA Corporation) (distearyl pentaerythritol diphosphite), and ADK STABPEP-36 (provided by ADEKA Corporation) (cyclicneopentanetetraylbis(2,6-di-t-butyl-4-methylphenyl) phosphite).

[Hydroxylamine-Based]

IRGASTAB FS 042 (provided by BASF) (N,N-dioctadecylhydroxylamine).

[Hindered Phenol/Phosphorus Mixture-Based Antioxidant]

IRGANOX B 225 (provided by BASF) (IRGAFOS168: IRGANOX1010=1:1),IRGANOX215 (provided by BASF) (IRGAFOS168: IRGANOX1010=2:1), IRGANOX220(provided by BASF) (IRGAFOS168: IRGANOX1010=3:1), and IRGANOX921(provided by BASF) (IRGAFOS168: IRGANOX1076=2:1).

[Oxygen Absorber]

In the present invention, the antioxidant is a concept covering anoxygen absorber. As the oxygen absorber, a typical oxygen absorberhaving a capacity to capture oxygen in the air can be used. Examplesthereof can include an iron powder oxygen absorber that absorbs oxygenin the air by way of oxidizing reaction of iron powder. Common use is acombination of 0.1 part by weight to 50 parts by weight of halogenatedmetal, for example, alkali metal such as sodium chloride, sodiumbromide, calcium chloride, and magnesium chloride, or a halide such aschloride, bromide and iodide of alkaline earth metal with 100 parts byweight of iron powder having a surface area of more than or equal to 0.5m²/g. This may be a mixture thereof or may be obtained by coating thesurface of iron powder with halogenated metal. It is noted that porousparticles, such as zeolite, impregnated with water content can befurther combined into the oxygen absorber used in the present inventionto further promote the aforementioned oxidation of iron by oxygen. Inparticular, a hindered phenolic antioxidant is preferable as a radicaltrap agent for a carbon radical.

In the present invention, at least one the above-mentioned ultravioletabsorbers and antioxidants can be used, or two or more of them can beused in combination. In particular, it is preferable to use abenzotriazol-based ultraviolet absorber and a hindered phenolicantioxidant in combination.

<Tackifier>

In the present invention, in at least one of the first layer and thesecond layer, the tackifier is blended by 0.1 part by mass to 100 partsby mass, preferably 1.0 part by mass to 20 parts by mass relative to 100mass of the thermoplastic elastomer component. Here, the tackifierrefers to a compounding agent for increasing tackiness of thethermoplastic elastomer composition. Examples of such a tackifier areillustrated below.

In the case of the first layer, it is necessary to maintain workability,productivity and gas barrier property while increasing vulcanizationadhesion with the second layer. On the other hand, in the case of thesecond layer, it is arranged between the first layer and the carcass plyto improve adhesive property with both of them and to maintainworkability, productivity and gas barrier property.

In the present embodiment, a tackifier similar to that of the secondembodiment can be used.

<Inner Liner>

(Polymer Layer Stack)

In the present invention, the inner liner employs the polymer layerstack formed of the first layer and the second layer. Here, the firstlayer and the second layer are elastomer compositions containingthermoplastic elastomer, and are in a softened state in a mold at avulcanizing temperature of, for example, 150° C. to 180° C. The softenedstate refers to an intermediate state between solid and liquid withimproved molecular mobility. When in the softened state, thethermoplastic elastomer compositions have improved reactivity ascompared with the solid state, and therefore stick or adhere to theadjacent component. Therefore, it is preferable to provide a coolingstep when manufacturing a tire in order to prevent change in shape ofthe thermoplastic elastomer compositions, adhesion and welding to theadjacent member. In the cooling step, after the tire vulcanization,quenching is performed for 10 seconds to 300 seconds to 50° C. to 120°C., so that the atmosphere in the bladder can be cooled. As a coolant,one or more of coolants selected from air, water vapor, water, and oilare used. The inner liner can be formed thin by adopting such coolingstep.

(Thickness of First Layer and Second Layer)

The thickness (Gs) in buttress region Rs of the inner liner shown inFIG. 1 is preferably made as thin as possible in a range that does notinhibit air permeability resistance, and is preferably set to fallwithin a range of 0.05 mm to 0.3 mm.

The entire first layer preferably has an average thickness of 0.05 mm to0.3 mm. If the average thickness of the first layer is less than 0.05mm, the first layer may be broken due to pressing pressure whenvulcanizing the raw tire in which the polymer layer stack formed of thefirst and second layers is applied to the inner liner, with the resultthat an air leakage phenomenon may take place in the resulting tire. Onthe other hand, if the average thickness of the first layer exceeds 0.3mm, the weight of the tire is increased to result in decreasedperformance in fuel efficiency. The average thickness of the first layermore preferably ranges from 0.05 mm to 0.15 mm. By adjusting the averagethickness of the first layer to fall within the above-mentioned range,flection durability of the buttress region can be improved whilemaintaining air permeability resistance.

The second layer preferably has an average thickness of 0.01 mm to 0.3mm. If the average thickness of the second layer is less than 0.01 mm,the second layer may be broken due to pressing pressure when vulcanizingthe raw tire in which the polymer layer stack is applied to the innerliner, with the result that vulcanization adhesion strength may bedecreased. On the other hand, if the average thickness of the secondlayer exceeds 0.3 mm, the weight of the tire is increased to possiblyresult in decreased performance in fuel efficiency. Further, the secondlayer more preferably has a thickness of 0.05 mm to 0.15 mm.

FIG. 2 shows an arrangement state of the inner liner with respect to thecarcass ply in the vulcanized tire. In FIG. 2, a polymer layer stack PLis composed of a first layer PL1 and a second layer PL2. When applyingpolymer layer stack PL to the inner liner of the pneumatic tire anddisposing second layer PL2 on the outer side in the tire radialdirection so as to be in contact with carcass ply 6, adhesive strengthbetween second layer PL2 and carcass 6 can be increased in the step ofvulcanizing the tire. In the resulting pneumatic tire, the inner linerand carcass ply 6 are adhered to each other in an excellent manner.Thus, the pneumatic tire has excellent air permeability resistance anddurability.

<Method for Manufacturing Pneumatic Tire>

The pneumatic tire of the present invention can be manufactured using ageneral manufacturing method. First, polymer layer stack PL describedabove is used to manufacture the inner liner. Pneumatic tire 1 can bemanufactured by applying the above-described inner liner to a raw tireand molding them through vulcanization together with other members. Whendisposing polymer layer stack PL in the raw tire, second layer PL2 isdisposed on the outer side in the tire radial direction so as to be incontact with carcass ply 6.

Example 1

The present invention will be described according to an Example.

<Isobutylene-Based Modified Copolymer>

(1) Component A-1: (styrene/β-pinene)-isobutylene-(styrene/β-pinene)block copolymer (having a β-pinene content of 9.7 percent by mass and anumber average molecular weight (Mn) of 103,000).

The method for producing component A-1 is as follows.

After the atmosphere in a 2-liter separable flask container wassubstituted by nitrogen, 31.0 mL of n-hexane dried with molecular sievesand 294.6 mL of butyl chloride similarly dried were added using asyringe. After immersing the polymerization container in a −70° C.mixture bath of dry ice and methanol for cooling, a deliver tube made ofTeflon (registered trademark) was connected to a pressure-resistantglass liquefaction collection tube with a three-way stop cock containing88.9 mL (941.6 mmol) of isobutylene monomer, and isobutylene monomer wasdelivered by nitrogen pressure into the polymerization container. Then,0.148 g (0.6 mmol) of p-dicumyl chloride and 0.07 g (0.8 mmol) ofα-picoline were added. Furthermore, 0.87 mL (7.9 mmol) of titaniumtetrachloride was to start polymerization. After 1.5 hours since thestart of polymerization, stirring was performed at a similartemperature, and then 1 mL of a polymerization solution was extractedfrom the polymerization solution as a sample. Then, after uniformlystirring 10.4 g (99.4 mmol) of styrene monomer and 6.8 g (49.7 mmol) ofβ-pinene having been cooled to −70° C., they were added to thepolymerization container. After 45 minutes since the addition of styreneand 3-pinene, about 40 mL of methanol was added to terminate thereaction. After evaporating a solvent and the like from the reactionsolution, the reaction solution was dissolved in toluene and washedtwice. Then, the toluene solution was added to a large amount ofmethanol to precipitate a polymer. A resultant product was vacuum driedat 60° C. for 24 hours. The molecular weight of the block copolymerobtained by the GPC method was measured. The number average molecularweight (Mn) thereof is 103,000, and Mw/Mn is 1.21.

(2) Component A-2: (styrene/β-pinene)-isobutylene-(styrene/β-pinene)block copolymer (having a β-pinene content of 5.3 percent by mass and anumber average molecular weight of 10,7000).

The method for producing component A-2 is as follows.

After the atmosphere in a 2-liter separable flask container wassubstituted by nitrogen, 31.0 mL of n-hexane dried with molecular sievesand 294.6 mL of butyl chloride similarly dried were added using asyringe. After immersing the polymerization container in a −70° C.mixture bath of dry ice and methanol for cooling, a deliver tube made ofTeflon (registered trademark) was connected to a pressure-resistantglass liquefaction collection tube with a three-way stop cock containing88.9 mL (941.6 mmol) of isobutylene monomer, and isobutylene monomer wasdelivered by nitrogen pressure into the polymerization container. Then,0.148 g (0.6 mmol) of p-dicumyl chloride and 0.07 g (0.8 mmol) ofα-picoline were added.

Next, 0.87 mL (7.9 mmol) of titanium tetrachloride was to startpolymerization. After 1.5 hours since the start of polymerization,stirring was performed at a similar temperature, and then 1 mL of apolymerization solution was extracted from the polymerization solutionas a sample. Then, after uniformly stirring 10.4 g (99.4 mmol) ofstyrene monomer and 3.6 g (26.3 mmol) of β-pinene having been cooled to−70° C., they were added to the polymerization container. After 45minutes since the addition of styrene and α-pinene, about 40 mL ofmethanol was added to terminate the reaction. After evaporating asolvent and the like from the reaction solution, the reaction solutionwas dissolved in toluene and washed twice. Furthermore, the toluenesolution was added to a large amount of methanol to precipitate apolymer. The resultant polymer was vacuum dried at 60° C. for 24 hours.The molecular weight of the block copolymer obtained by the GPC methodwas measured. The number average molecular weight (Mn) of the blockcopolymer is 107,000, and Mw/Mn is 1.23.

(3) Component A-3: styrene-(isobutylene/β-pinene)-styrene blockcopolymer (having a β-pinene content of 5.3 percent by mass and a numberaverage molecular weight of 10,9000).

The method for producing of component A-3 is as follows.

After the atmosphere in a 2-liter separable flask container wassubstituted by nitrogen, 31.0 mL of n-hexane dried with molecular sievesand 294.6 mL of butyl chloride dried with molecular sieves were addedusing a syringe. After immersing the polymerization container in a −70°C. mixture bath of dry ice and methanol for cooling, 3.6 g (26.3 mmol)of (β-pinene was added.

Then, a deliver tube made of Teflon (registered trademark) was connectedto a pressure-resistant glass liquefaction collection tube with athree-way stop cock containing 88.9 mL (941.6 mmol) of isobutylenemonomer, and isobutylene monomer was delivered by nitrogen pressure intothe polymerization container. Then, 0.148 g (0.6 mmol) of p-dicumylchloride and 0.07 g (0.8 mmol) of α-picoline were added. Furthermore,0.87 mL (7.9 mmol) of titanium tetrachloride was to startpolymerization. After 45 minutes since the start of polymerization, 10.4g (99.4 mmol) of styrene monomer having been cooled to −70° C. was addedto the polymerization container. After 45 minutes since the addition ofstyrene, about 40 mL of methanol was added to terminate the reaction.After evaporating a solvent and the like from the reaction solution, thereaction product was dissolved in toluene and washed twice. Furthermore,the toluene solution was added to a large amount of methanol toprecipitate a polymer. The resultant polymer was vacuum dried at 60° C.for 24 hours. The molecular weight of a block copolymer obtained by theGPC method was measured. The number average molecular weight (Mn) of theblock copolymer is 109,000, and Mw/Mn is 1.21.

<SIBS (Styrene-Isobutylene-Styrene Block Copolymer)>

“SIBSTAR 102T (Shore A hardness: 25; the content of the styrenecomponent: 15 percent by mass; and weight average molecular weight:100,000)” provided by Kaneka Corporation was used.

<IIR>

“Exxon Chlorobutyl 1066” provided by Exxon Mobil Corporation was used.

<IIR>

TSR20 was used for the natural rubber.

<Filler>

Carbon black, “SEAST V” (N660, N₂SA: 27 m²/g) provided by Tokai CarbonCo., Ltd. was used for the filler.

<Adjustment of Elastomer Composition>

Thermoplastic elastomer compositions were prepared by blending theabove-described elastomer components as indicated in Tables 1 and 2.

TABLE 1 Com- Com- Com- Com- Com- Com- parative parative parativeparative parative parative Example Example Example Example ExampleExample 1-1 1-2 1-3 1-4 1-5 1-6 Inner Liner Blending Polymer MixtureSIBS — 100 90 90 90 10 Amount Component Component A-1 — — 10 — — 90(parts by Component A-2 — — — 10 — — mass) Component A-3 — — — — 10 —IIR 80 — — — — — NR 20 — — — — — Layer Filler 60 — — — — — ThicknessIIR/NR/Filler Layer 1.00 — — — — — (mm) SIBS Layer — 0.60 — — — — MixedLayer of SIBS + Component A — — 0.60 0.60 0.60 0.60 Gs/Gb Ratio 1.001.00 1.00 1.00 1.00 1.00 Gs (mm) 1.00 0.60 0.60 0.60 0.60 0.60Performance Detachment Force index 100 60 105 105 102 109 EvaluationFlection Fatigue Resistance index 100 105 105 105 105 101 Static AirPressure Decreasing Ratio (%/month) 3.2 2.5 2.5 2.5 2.5 2.7 CrackResistance index 100 100 100 100 100 100 Com- Com- Com- Com- Com-parative parative parative parative parative Example Example ExampleExample Example 1-7 1-8 1-9 1-10 1-11 Inner Liner Blending PolymerMixture SIBS 10 10 95 5 90 Amount Component Component A-1 — — 5 95 10(parts by Component A-2 90 — — — — mass) Component A-3 — 90 — — — IIR —— — — — NR — — — — — Layer Filler — — — — — Thickness IlR/NR/FillerLayer — — — — — (mm) SIBS Layer — — — — — Mixed Layer of SIBS +Component A 0.60 0.60 0.60 0.60 0.60 Gs/Gb Ratio 1.00 1.00 0.75 0.750.25 Gs (mm) 0.60 0.60 0.45 0.45 0.15 Performance Detachment Force index106 105 90 105 105 Evaluation Flection Fatigue Resistance index 101 101104 101 105 Static Air Pressure Decreasing Ratio (%/month) 2.7 2.7 2.52.7 2.5 Crack Resistance index 100 100 100 98 95

TABLE 2 Example Example Example Example Example 1-1 1-2 1-3 1-4 1-5Inner Liner Blending Polymer Mixture SIBS 90 90 90 10 10 AmountComponent Component A-1 10 — — 90 — (parts by Component A-2 — 10 — — 90mass) Component A-3 — — 10 — — IIR — — — — — NR — — — — — Filler — — —Layer IIR/NR/Filler Layer — — — — — Thickness SIBS Layer — — — — — (mm)Mixed Layer of SIBS + Component A 0.60 0.60 0.60 0.60 0.60 Gs/Gb Ratio0.75 0.75 0.75 0.75 0.75 Gs (mm) 0.45 0.45 0.45 0.45 0.45 PerformanceDetachment Force index 105 105 102 109 106 Evaluation Flection FatigueResistance index 105 105 105 101 101 Static Air Pressure DecreasingRatio (%/month) 2.5 2.5 2.5 2.7 2.7 Crack Resistance index 110 110 110110 110 Example Example Example Example 1-6 1-7 1-8 1-9 Inner LinerBlending Polymer Mixture SIBS 10 90 90 90 Amount Component Component A-1— 10 10 10 (parts by Component A-2 — — — — mass) Component A-3 90 — — —IIR — — — — NR — — — — Filler — — — — Layer IIR/NR/Filler Layer — — — —Thickness SIBS Layer — — — — (mm) Mixed Layer of SIBS + Component A 0.600.60 0.60 0.60 Gs/Gb Ratio 0.75 0.58 0.50 0.33 Gs (mm) 0.45 0.35 0.300.20 Performance Detachment Force index 105 105 105 105 EvaluationFlection Fatigue Resistance index 101 105 105 105 Static Air PressureDecreasing Ratio (%/month) 2.7 2.5 2.5 2.5 Crack Resistance index 110110 108 104

<Method for Manufacturing Inner Liner>

Based on the blends of Tables 1 and 2, an isobutylene-based modifiedcopolymer (component A) and the elastomer component of the SIBS wereintroduced into a biaxial extruder (screw diameter: φ50 mm; L/D: 30;cylinder temperature: 220° C.) to obtain a pellet of an elastomercomposition. Thereafter, a sheet for an inner liner was fabricated usinga T-die extruder (screw diameter: φ80 mm; L/D: 50; die gap width: 500mm; cylinder temperature: 220° C.).

<Manufacturing of Pneumatic Tire>

A raw tire was prepared using the sheet for an inner liner obtained bythe above-described method. Then, in the vulcanization step, the rawtire was press molded at 170° C. for 20 minutes. After vulcanization ofthe tire, the tire was cooled for 3 minutes at 100° C., and thevulcanized tire was removed from the mold. A pneumatic tire with a sizeof 195/65R15 having the basic structure shown in FIG. 1 was thusmanufactured.

Comparative Examples 1-1 to 1-11

In Tables 1 and 2, the thickness of a mixed layer of SIBS+component Aindicates the average thickness of a region other than Gs. Gb was 0.6 mmin each of the Examples and Comparative Examples except ComparativeExample 1-1.

For the inner liner of Comparative Example 1-1, the following blendingcomponents were mixed with a Banbury mixer, and a sheet was formedtherefrom using a calender roll, thereby obtaining a polymer film havinga thickness of 1.0 mm. The value of Gs/Gb was 1.

IIR (Note 1) 80 parts by mass NR (Note 2) 20 parts by mass Filler (Note3) 60 parts by mass (Note 1) “Exxon Chlorobutyl 1068” provided by ExxonMobil Corporation (Note 2) TSR20 (Note 3) “SEAST V” (N660; nitrogenadsorption specific surface area: 27 m²/g) provided by Tokai Carbon Co.,Ltd.

In Comparative Example 1-2, the SIBS layer produced by theabove-described method and having a thickness of 0.6 mm was used as theinner liner. The value of Gs/Gb was 1. Comparative Examples 1-3 to 1-8are examples in which an elastomer composition obtained by mixing anisobutylene-based modified copolymer (component A) with the SIBS wasused for the inner liner, and the value of Gs/Gb was 1. ComparativeExample 1-9 is an example in which component A was mixed by 5 percent bymass with the SIBS. Comparative Example 1-10 is an example in whichcomponent A was mixed by 95 percent by mass with the SIBS, and the valueof Gs/Gb was 0.75. Comparative Example 1-11 is an example in whichcomponent A was mixed with the SIBS, and the value of Gs/Gb was 0.25.

Examples 1-1 to 1-9

Examples 1-1 to 1-6 are examples in which an elastomer compositionobtained by mixing an isobutylene-based modified copolymer (component A)with the SIBS was used for the inner liner, and the value of Gs/Gb was0.75.

Examples 1-1 and 1-7 to 1-9 are examples in which an elastomercomposition obtained by mixing component A with the SIBS was used forthe inner liner, and the value of Gs/Gb were varied. The value of Gs/Gbof Example 1-11 was 0.75, which is the highest, and the value of Gs/Gbof Example 1-9 was 0.33, which is the lowest.

<Performance Test>

For each of the sheets and pneumatic tires of the Examples andComparative Examples, a performance test was conducted by the followingmethod.

<Detachment Test>

In accordance with JISK-6256 “Rubber, vulcanized orthermoplastic—Determination of adhesion test”, a test specimen wasprepared and a detachment test was performed. Detachment force betweenthe inner liner and the carcass was measured. The test specimen had awidth of 25 mm. The detachment test was performed under a roomtemperature condition of 23° C. A larger detachment force between theinner liner and the carcass is more preferable.

<Flection Fatigue Resistance Test>

In accordance with JISK-6260 “Rubber, vulcanized orthermoplastic—Determination of flex cracking and crack growth (De Mattiatype)”, a predetermined test specimen having a groove at its center wasfabricated. For the inner liner, a sheet having a thickness of 0.3 mmwas adhered to a rubber and was vulcanized, thereby fabricating apredetermined test specimen. The test was performed in the followingmanner. That is, a cut was provided in advance at the center of thegroove of the test specimen, flection deformation was repeatedly given,and crack growth was measured. At an atmospheric temperature of 23° C.,a strain of 30%, and a cycle of 5 Hz, the crack length was measured atthe 700,000-th cycle, the 1,400,000-th cycle, and the 2,100,000-thcycle. The number of repetitions of flection deformation for 1 mm growthof the crack was calculated. With the value of Comparative Example 1-1being regarded as a reference (100), the flection fatigue resistance ofthe polymer layer stack of each of the Examples and Comparative Exampleswas indicated by an index. It can be said that as the numerical value islarger, the crack is less likely to be grown, which is more favorable.For example, the index of Example 1-1 is obtained from the followingequation:

(Flection Fatigue Resistance Index)=(Number of Repetitions of FlectionDeformation of Example 1-1)/(Number of Repetitions of FlectionDeformation of Comparative Example 1-1)×100

<Static Air Pressure Decreasing Ratio Test>

A 195/65R15 steel radial PC tire produced by the above-described methodwas assembled to a JIS specification rim 15×6JJ, and air was introducedthereinto at an initial air pressure of 300 Kpa. Then, the tire was leftfor 90 days at a room temperature, and the air pressure decreasing ratiowas calculated.

<Measurement of Average Thickness>

The 195/65R15 steel radial PC tire was equally divided into eight in thecircumferential direction. In each of the divided portions, eight cutsamples were made by cutting it in the tire radial direction with awidth of 20 mm. For each of the eight cut samples, the thickness of theinner liner was measured at five points with an equal interval in eachof buttress region Rs and bead region Rb. Arithmetic mean values of themeasured values at the total of 40 points each were determined as Gs andGb, respectively.

<Crack Resistance>

The 195/65R15 steel radial PC tire was assembled to the JISspecification rim 15×6JJ, and air was introduced at a proper airpressure. Then, the maximum load corresponding to this air pressure wasapplied in accordance with the air pressure-loading capabilitycorrespondence table of the JATMA YEAR BOOK, and traveling was performedon a drum at a speed of 80 km/h. Then, the traveling was terminated uponoccurrence of damage that could be identified by visual observation onthe external appearance, and the traveling distance was obtained. Thetraveling distance is indicated by an index with the traveling distanceof Comparative Example 1-1 being regarded as 100. As the index islarger, the crack resistance is more excellent.

<Result of Performance Evaluation>

It can be seen from Tables 1 and 2 that all of Examples 1-1 to 1-9 ofthe present invention are totally superior to Comparative Examples 1-1to 1-11 in detachment force, flection fatigue resistance, static airdecreasing ratio, and crack resistance.

Example 2

In accordance with the specifications shown in Tables 3 and 4, pneumatictires of the Examples and Comparative Examples were manufactured andperformance was evaluated. The SIBS and the modified SIBS used for thepolymer sheet were prepared as follows.

[SIBS]

“SIBSTAR 102T (Shore A hardness: 25; the content of the styrenecomponent: 15 percent by mass; and weight average molecular weight:100,000)” provided by Kaneka Corporation was used.

[Production of SIBS Modified Copolymer]

Into a 2-liter separable flask, 75 g of a styrene-isobutylene blockcopolymer (the styrene content: 30%; the number of moles of the styreneunit: 0.216 mol) was input, and the atmosphere in the container wassubstituted by nitrogen. Using a syringe, 1200 mL of n-hexane dried withmolecular sieves and 1800 ml of n-butyl chloride dried with molecularsieves were added.

Next, 30 g (0.291 mol) of methacrylic acid chloride was added using asyringe. Then, 39.4 g (0.295 mol) of aluminum trichloride was addedwhile stirring the solution to start a reaction. After the reaction for30 minutes, about 1000 ml of water was added to the reaction solution,which was stirred vigorously to terminate the reaction. The reactionsolution was washed with a large amount of water several times, andfurther slowly dropped into a large amount of a methanol-acetone mixedsolvent (1:1) to precipitate a reaction product. Then, the reactionproduct was vacuum dried at 60° C. for 24 hours to obtain an SIBSmodified copolymer (weight average molecular weight: 150,000; thestyrene content: 20 percent by mass; acid chloride: 1.0 percent byweight).

<Manufacturing of Pneumatic Tire>

The above-described SIBS and modified SIBS were pelletized using abiaxial extruder (screw diameter: φ50 mm; L/D: 30; cylinder temperature:220° C.). Thereafter, the polymer sheet was fabricated using a T-dieextruder (screw diameter: φ80 mm; L/D: 50; die gap width: 500 mm;cylinder temperature: 220° C.; film gauge: 0.3 mm).

The pneumatic tire was manufactured as follows. That is, theabove-described polymer sheet was used for the inner liner, and a rawtire having the basic structure shown in FIG. 1 with the size of195/65R15 was molded. Then, in the vulcanization step, the raw tire wasmolded at 170° C. for 20 minutes. Then, in the pneumatic tire, thebladder was cooled to be quenched for 10 seconds to 300 seconds to 50°C. to 120° C. Water was used as a coolant. Here, in order to adjust thethickness of the inner liner in bead region Rb and buttress region Rs, aprofile was provided at an extrusion opening for the polymer sheet,whereby a sheet in which thickness Gs in the buttress region was madethin was obtained in one piece. This was disposed on the tire innersurface as the inner liner.

TABLE 3 Com- Com- Com- Com- Com- Com- parative parative parativeparative parative parative Example Example Example Example ExampleExample 2-1 2-2 2-3 2-4 2-5 2-6 Inner Liner Blending Polymer MixtureSIBS — 100 90 90 50 50 Amount Component SIBS Modified — — 10 10 50 50(parts by Copolymer mass) Tackifier — — — 5 — 5 Chlorobutyl 80 — — — — —NR 20 — — — — — Filler 60 — — — — — Layer IIR/NR/Filler Layer 1.00 — — —— — Thickness SIBS Layer/SIBS Modified — 0.60⁽*¹⁾ 0.60 — 0.60 — (mm)Copolymer Layer Gb SIBS Modified Copolymer/ — — — 0.60 — 0.60SIBS/Tackifier Mixed Layer Gs (mm) 1.00 0.60 0.60 0.60 0.60 0.60 Gs/GbRatio (—) 1.00 1.00 1.00 1.00 1.00 1.00 Performance Detachment Forceindex 100 60 100 103 105 108 Evaluation Flection Fatigue Resistanceindex 100 105 105 105 105 105 Static Air Pressure Decreasing Ratio(%/month) 3.2 2.5 2.5 2.5 2.6 2.6 Crack Resistance index 100 100 100 100100 100 Com- Com- Com- Com- Com- parative parative parative parativeparative Example Example Example Example Example 2-7 2-8 2-9 2-10 2-11Inner Liner Blending Polymer Mixture SIBS — — 95 95 90 Amount ComponentSIBS Modified 100 100 5 5 10 (parts by Copolymer mass) Tackifier — 5 — 55 Chlorobutyl — — — — — NR — — — — — Filler — — — — Layer IIR/NR/FillerLayer — — — — — Thickness SIBS Layer/SIBS Modified 0.60⁽*²⁾ — 0.60 — —(mm) Copolymer Layer Gb SIBS Modified Copolymer/ — 0.60 — 0.60 0.60SIBS/Tackifier Mixed Layer Gs (mm) 0.60 0.60 0.45 0.45 0.15 Gs/Gb Ratio(—) 1.00 1.00 0.75 0.75 0.25 Performance Detachment Force index 110 11380 85 103 Evaluation Flection Fatigue Resistance index 103 103 104 104100 Static Air Pressure Decreasing Ratio (%/month) 2.6 2.6 2.5 2.5 2.5Crack Resistance index 100 100 100 100 95 ⁽*¹⁾Single layer of SIBS⁽*²⁾Single layer of SIBS modified copolymer

TABLE 4 Example Example Example Example Example 2-1 2-2 2-3 2-4 2-5Inner Liner Blending Polymer Mixture SIBS 90 90 50 50 — Amount ComponentSIBS Modified 10 10 50 50 100 (parts by Copolymer mass) Tackifier 5 — 5— 5 Chlorobutyl — — — — — NR — — — — — Filler — — — — — LayerIIR/NR/Filler Layer — — — — — Thickness SIBS Layer/SIBS Modified — 0.60— 0.60 — (mm) Copolymer Layer Gb SIBS Modified Copolymer/SIBS/ 0.60 —0.60 — 0.60 Tackifier Mixed Layer Gs (mm) 0.45 0.45 0.45 0.45 0.45 Gs/GbRatio (—) 0.75 0.75 0.75 0.75 0.75 Performance Detachment Force index103 100 108 105 113 Evaluation Flection Fatigue Resistance index 105 105105 105 103 Static Air Pressure Decreasing Ratio (%/month) 2.5 2.5 2.62.6 2.6 Crack Resistance index 110 110 110 110 110 Example ExampleExample Example 2-6 2-7 2-8 2-9 Inner Liner Blending Polymer MixtureSIBS — 90 90 90 Amount Component SIBS Modified 100 10 10 10 (parts byCopolymer mass) Tackifier — 5 5 5 Chlorobutyl — — — — NR — — — — Filler— — — — Layer IIR/NR/Filler Layer — — — — Thickness SIBS Layer/SIBSModified 0.60⁽*¹⁾ — — — (mm) Copolymer Layer Gb SIBS ModifiedCopolymer/SIBS/ — 0.60 0.60 0.60 Tackifier Mixed Layer Gs (mm) 0.45 0.350.30 0.20 Gs/Gb Ratio (—) 0.75 0.58 0.50 0.33 Performance DetachmentForce index 110 103 103 103 Evaluation Flection Fatigue Resistance index103 105 105 105 Static Air Pressure Decreasing Ratio (%/month) 2.6 2.52.5 2.5 Crack Resistance index 110 110 108 105 ⁽*¹⁾Single layer of SIBSmodified copolymer

In each of Tables 3 and 4, the thickness of the inner liner representsthe thickness of a region other than Gb. Gb was 0.6 mm in each of theExamples and Comparative Examples except Comparative Example 2-1.

<Rubber Sheet for Carcass Ply>

In the Examples, a topping rubber for the carcass ply was blended asfollows.

<Blend A of Topping Rubber>

Natural rubber (Note 1) 70 parts by mass Synthetic rubber (SBR1502) 30parts by mass Carbon black (Note 2) 45 parts by mass Zinc oxide  3 partsby mass Sulfur  3 parts by mass Vulcanization accelerator (Note 3)  1part by mass Vulcanization aid  1 part by mass (Note 1) TSR20 (Note 2)“SEAST 3” (N330) provided by Tokai Carbon Co., Ltd. (Note 3) “NOCCELERCZ” provided by Ouchi Shinko Chemical

Comparative Example 2-1

For the inner liner of Comparative Example 2-1, the following blendingcomponents were mixed with a Banbury mixer, and formed into a sheet witha calender roll, thereby obtaining a polymer film having a thickness of1.0 mm. The value of Gs/Gb was 1.

Chlorobutyl (Note 1) 80 parts by mass Natural rubber (Note 2) 20 partsby mass Filler (Note 3) 60 parts by mass (Note 1) “Exxon Chlorobutyl1068” provided by Exxon Mobil Corporation (Note 2) TSR20 (Note 3) “SEASTV” (N660; nitrogen adsorption specific surface area: 27 m²/g) providedby Tokai Carbon Co., Ltd.

Comparative Examples 2-2, 2-7

In Comparative Example 2-2, the SIBS was used for the polymer sheet. InComparative Example 2-7, the modified SIBS was used for the polymersheet. They had a thickness (Gb) of 0.6 mm. The value of Gs/Gb was 1.

Comparative Examples 2-3 to 2-6, 2-8

A polymer sheet of a mixture of the modified SIBS and the SIBS or amixture further containing a tackifier having a thickness (Gb) of 0.60mm was applied to the inner liner. The value of Gs/Gb was 1.

Comparative Examples 2-9 to 2-11

A polymer sheet of a mixture of the modified SIBS and the SIBS or amixture further containing a tackifier having a thickness (Gb) of 0.60mm was applied to the inner liner. The value of Gs/Gb was 0.75.

Examples 2-1, 2-3, 2-7 to 2-9

Examples 2-1, 2-3 and 2-7 to 2-9 are examples in which the SIBS, themodified SIBS and a tackifier were mixed into the polymer sheet. InExamples 2-7 to 2-9, the value of Gs/Gb were varied.

Examples 2-2, 2-4, 2-5, 2-6

Examples 2-2 and 2-4 are examples in which the SIBS and the modifiedSIBS were mixed into the polymer sheet. The value of Gs/Gb was 0.75 ineach example.

Examples 2-5 and 2-6 are examples in which the modified SIBS was mixedor the tackifier was further mixed into the polymer sheet. The value ofGs/Gb was 0.75 in each example.

It can be seen that all of the Examples of the present invention aresuperior to Comparative Example 2-1 in detachment force, flectionfatigue resistance, static air pressure decreasing ratio, and crackresistance.

<Performance Test>

The method for the performance test on each of the pneumatic tires ofthe Examples and Comparative Examples will be described below.

<Detachment Test>

In accordance with JIS-K6256 “Rubber, vulcanized orthermoplastic—Determination of adhesion test”, a detachment test wasperformed to measure detachment force between the inner liner and thecarcass (IL/carcass detachment force). The test specimen had a width of25 mm. The detachment test was performed under a room temperaturecondition of 23° C. Larger detachment force between the inner liner andthe carcass is more preferable.

<Flection Fatigue Resistance Test>

In accordance with JIS-K6260 “Rubber, vulcanized orthermoplastic—Determination of flex cracking and crack growth (De Mattiatype)”, a predetermined test specimen having a groove at its center wasfabricated. For the inner liner, a sheet having a thickness of 0.3 mmwas adhered to a rubber and was vulcanized, thereby fabricating apredetermined test specimen. The test was performed in the followingmanner. That is, a cut was provided in advance at the center of thegroove of the test specimen, flection deformation was repeatedly given,and crack growth was measured. At an atmospheric temperature of 23° C.,a strain of 30%, and a cycle of 5 Hz, the crack length was measured atthe 700000-th cycle, the 1400000-th cycle, and the 2100000-th cycle. Thenumber of repetitions of flection deformation for 1 mm growth of thecrack was calculated. With the value of Comparative Example 2-1 beingregarded as a reference (100), the flection fatigue resistance of eachof the Examples and Comparative Examples was indicated by an index. Itcan be said that as the numerical value is larger, the crack is lesslikely to be grown, which is more favorable. For example, the index ofExample 2-1 can be obtained by the following equation:

(Flection Fatigue Resistance Index)=(Number of Repetitions of FlectionDeformation of Example 2-1)/(Number of Repetitions of FlectionDeformation of Comparative Example 2-1)×100

<Static Air Pressure Decreasing Ratio Test>

A 195/65R15 steel radial PC tire was assembled to a JIS specificationrim 15×6JJ, and air was introduced thereinto at an initial air pressureof 300 Kpa. Then, the tire was left for 90 days at a room temperature,and the air pressure decreasing ratio was calculated.

<Measurement of Average Thickness>

The 195/65R15 steel radial PC tire was equally divided into eight in thecircumferential direction. In each of the divided portions, eight cutsamples were made by cutting it in the tire radial direction with awidth of 20 mm. For each of the eight cut samples, the thickness of theinner liner was measured at five points with an equal interval in eachof buttress region Rs and bead region Rb. Arithmetic mean values of themeasured values at the total of 40 points each were determined as Gs andGb, respectively.

<Crack Resistance>

The 195/65R15 steel radial PC tire was assembled to the JISspecification rim 15×6JJ, and air was introduced at a proper airpressure. Then, the maximum load corresponding to this air pressure wasapplied in accordance with the air pressure-loading capabilitycorrespondence table of the JATMA YEAR BOOK, and traveling was performedon a drum at a speed of 80 km/h. Then, the traveling was terminated uponoccurrence of damage that could be identified by visual observation onthe external appearance. Then, the traveling distance was obtained. Thetraveling distance is indicated by an index with the traveling distanceof Comparative Example 2-1 being regarded as 100. As the index islarger, the crack resistance is more excellent.

Example 3

<Polymer Layer Stack>

The thermoplastic elastomers (SIB, SIBS, SIS, and SIBS modifiedcopolymer), ultraviolet absorber and antioxidant used for manufacturingthe polymer layer stack formed of the first layer and the second layerof the present invention were prepared in the following manner.

[SIB]

Into a 2 L reaction container having an agitator, 589 mL ofmethylcyclohexane (dried with molecular sieves), 613 ml of n-butylchloride (dried with molecular sieves), and 0.550 g of cumyl chloridewere added. The reaction container was cooled to −70° C., and then 0.35mL of α-picoline (2-methylpyridine) and 179 mL of isobutylene wereadded. Further, 9.4 mL of titanium tetrachloride was added to startpolymerization. They were reacted with each other for 2.0 hours whilestirring the solution at −70° C. Next, 59 mL of styrene was added to thereaction container, and the reaction was continued for another 60minutes. Then, a large amount of methanol was added to stop thereaction. After removing the solvent and the like from the reactionsolution, the polymer was dissolved with toluene and washed with watertwice. This toluene solution was added to a methanol mixture toprecipitate a polymer. The resultant polymer was dried at 60° C. for 24hours, thereby obtaining a styrene-isobutylene diblock copolymer (thecontent of the styrene component: 15 percent by mass; weight averagemolecular weight: 70,000).

[SIBS]

“SIBSTAR 102T (Shore A hardness: 25; the content of the styrenecomponent: 15 percent by mass; and weight average molecular weight:100,000)” provided by Kaneka Corporation was used.

[SIS]

D161JP (the content of the styrene component: 15 percent by mass; weightaverage molecular weight: 150,000) provided by Kraton Polymers was used.

[Production of SIBS Modified Copolymer]

Into a 2-liter separable flask, 75 g of a styrene-isobutylene blockcopolymer (the styrene content: 30%; the number of moles of the styreneunit: 0.216 mol) was input, and the atmosphere in the container wassubstituted by nitrogen. Using a syringe, 1200 mL of n-hexane dried withmolecular sieves and 1800 ml of n-butyl chloride dried with molecularsieves were added.

Next, 30 g (0.291 mol) of methacrylic acid chloride was added using asyringe. Then, 39.4 g (0.295 mol) of aluminum trichloride was addedwhile stirring the solution to start a reaction. After the reaction for30 minutes, about 1000 ml of water was added to the reaction solution,which was stirred vigorously to terminate the reaction. The reactionsolution was washed with a large amount of water several times, andfurther slowly dropped into a large amount of a methanol-acetone mixedsolvent (1:1) to precipitate a reaction product. Then, the reactionproduct was vacuum dried at 60° C. for 24 hours to obtain a SIBSmodified copolymer (weight average molecular weight: 150,000; thestyrene content: 20 percent by weight; acid chloride: 1.0 percent byweight).

[Ultraviolet Absorber]

As a benzotriazol-based ultraviolet absorber, “ADK STAB LA-36” providedby ADEKA Corporation(2-(2′-hydroxy-3′-ter-butyl-5′-methylphenyl)-5-chlorobenzotriazol) wasused. This ultraviolet absorber has a melting point of 138° C. to 141°C., a molecular weight of 315.8, and a maximum absorption wavelength of353 nm.

[Antioxidant]

As a hindered phenolic antioxidant, “IRGANOX1010” provided by BASF(pentaerythrityl tetrakis (3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) was used. This antioxidant has a melting point of 110 IC to125° C., a specific gravity of 1.15, and a molecular weight of 117.7.

TABLE 5 Blending Example Comparative Blend Example Blend of First Layer1 2 3 1 2 3 4 SIBS (percent 100 100 — 100 — 50 50 by mass) SIBS (percent— — 100 — 100 50 50 Modified by mass) Tackifier (percent — — — — — 10 10by mass) Polyiso- (percent — — — — — 10 10 butylene by mass) Ultraviolet(percent 0.4 0.4 — 0.5 0.5 0.5 20 Absorber by mass) Antioxidant (percent— — 0.4 0.5 0.5 0.5 20 by mass)

TABLE 6 Blending Example Comparative Blend Example Blend of Second Layer4 5 6 5 6 7 8 9 10 SIS (percent 100 100 — 100 — 50 50 35 35 by mass) SIB(percent — — 100 — 100 — — — — by mass) SIBS (percent — — — — — 50 50 3535 by mass) SIBS Modified (percent — — — — — — 30 30 by mass) Tackifier(percent — — — — — — 10 10 — by mass) Polyisobutylene (percent — — — — —— 10 10 — by mass) Ultraviolet (percent — 0.4 — 0.5 0.5 0.5 20 20 45Absorber by mass) Antioxidant (percent — — 0.4 0.5 0.5 0.5 20 20 45 bymass) (Note 1) Tackifier: C9 petroleum resin, ARKON P140 (provided byArakawa Chemical Industries Co., Ltd., softening point: 140° C.; weightaverage molecular weight Mw: 900). (Note 2) Polyisobutylene: “Tetrax 3T”provided by Nippon Oil Corporation (viscosity average molecular weight:30,000; weight average molecular weight: 49,000).

<Method for Manufacturing Inner Liner>

Based on Example Blends and Comparative Blends shown in Tables 5 and 6,thermoplastic elastomer compositions such as the SIBS modifiedcopolymer, SIBS, SIS, and SIB were pelletized using a biaxial extruder(screw diameter: φ50 mm; L/D: 30; cylinder temperature: 220° C.).Thereafter, the inner liner was fabricated using a T-die extruder (screwdiameter: φ80 mm; L/D: 50; die gap width: 500 mm; cylinder temperature:220° C.; film gauge for the first layer: 0.25 mm; film gauge for each ofthe second layer: 0.05 mm).

Here, in order to adjust the thickness of the inner liner in bead partregion Rb and buttress region Rs, a profile was provided at an extrusionopening for the polymer sheet, whereby a sheet in which thickness Gs inthe buttress region was made thin was obtained in one piece. This wasdisposed on the tire inner surface as the inner liner.

<Manufacturing of Pneumatic Tire>

A pneumatic tire of size of 195/65R15 having the basic structure shownin FIG. 1 was manufactured. That is, the above-described polymer layerstack was used for the inner liner to manufacture a raw tire, and theraw tire was press vulcanized at 170° C. for 20 minutes. After coolingat 110° C. for 3 minutes without removing the vulcanized tire from thevulcanization mold, the vulcanized tire was removed from thevulcanization mold. Water was used as a coolant.

Table 5 shows details of Comparative Blends 1 to 6 and Example Blends 1to 8 of the first layer, and Table 6 shows details of Comparative Blends7 to 13 and Example Blends 9 to 17 of the second layer. Thesecompositions were used for the first layer and the second layer tomanufacture tires of Examples and Comparative Examples. Theirspecifications and the result of performance evaluations are shown inTables 7 and 8.

Comparative Examples 3-1 to 3-5, Examples 3-1 to 3-9

In Table 7, each of Comparative Examples 3-1 and 3-2 is an example innerliner in which the SIBS was used for the first layer, the SIS was usedfor the second layer, and Gs/G was 1 and 0.5, respectively. ComparativeExample 3-3 is an example inner liner in which the SIBS was used for thefirst layer and the SIS was used for the second layer. ComparativeExample 3-4 is an example inner liner in which the SIBS was used for thefirst layer and the SIB was used for the second layer. ComparativeExample 3-5 is an example inner liner in which the SIBS modifiedcopolymer was used for the first layer and the SIS was used for thesecond layer.

Examples 3-1 to 3-4 are example inner liners in which the SIS was usedfor the second layer and blends (Example Blends 1 to 4) with differentelastomer components were used for the first layer. Examples 3-5 to 3-9are example inner liners in which the SIBS was used for the first layerand blends (Example Blends 6 to 10) with different elastomer componentswere used for the second layer. It can be seen that Examples 3-1 to 3-9of the present invention are totally excellent in weather resistance,flection crack growth resistance, air permeability resistance, androlling resistance.

Comparative Example 3-6, Examples 3-10 to 3-13

In Table 8, Comparative Example 3-6 is an example inner liner in whichthe same blends as those in Example 3-4 were used for first layer andthe second layer, and Gs/G was 1. Examples 3-10 to 3-13 are exampleinner liners in which the same blends as those in Comparative Example3-6 were used for first layer and the second layer, and the value ofGs/G was varied. It can be seen that Examples 3-10 to 3-13 are totallysuperior to Comparative Example 3-6 in weather resistance, flectioncrack growth resistance, air permeability resistance, and rollingresistance.

TABLE 7 Comparative Comparative Comparative Comparative ComparativeExample 3-1 Example 3-2 Example 3-3 Example 3-4 Example 3-5 Constitutionof First Layer Thickness (mm) 0.6 0.3 0.3 0.3 0.3 Inner Liner Layer UsedBlend Comparative Comparative Comparative Comparative Comparative Blend1 Blend 1 Blend 2 Blend 2 Blend 3 Second Layer Thickness (mm) 0.3 0.10.1 0.1 0.1 Layer Used Blend Comparative Comparative ComparativeComparative Comparative Blend 4 Blend 4 Blend 4 Blend 6 Blend 5 ButtressThickness Ratio Gs/Gb 1 0.5 0.5 0.5 0.5 Portion Thickness Gs (mm) 0.90.2 0.2 0.2 0.2 Performance Weather Resistance (index) 100 100 102 103103 Evaluation Flection Crack Growth Test (index) 100 105 110 115 118Static Air Pressure Decreasing Ratio 2.7 2.7 2.7 2.7 2.7 RollingResistance (index) 100 102 102 102 102 Overall Judgment B B B B BExample Example Example Example Example 3-1 3-2 3-3 3-4 3-5 Constitutionof First Layer Thickness (mm) 0.3 0.3 0.3 0.3 0.3 Inner Liner Layer UsedBlend Example Example Example Example Example Blend 1 Blend 2 Blend 3Blend 4 Blend 1 Second Layer Thickness (mm) 0.1 0.1 0.1 0.1 0.1 LayerUsed Blend Example Example Example Example Example Blend 5 Blend 5 Blend5 Blend 5 Blend 6 Buttress Thickness Ratio Gs/Gb 0.5 0.5 0.5 0.5 0.5Portion Thickness Gs (mm) 0.2 0.2 0.2 0.2 0.2 Performance WeatherResistance (index) 120 120 120 136 120 Evaluation Flection Crack GrowthTest (index) 128 130 129 166 130 Static Air Pressure Decreasing Ratio2.7 2.7 2.7 2.7 2.7 Rolling Resistance (index) 102 102 102 102 102Overall Judgment A A A A Example Example Example Example 3-6 3-7 3-8 3-9Constitution of First Layer Thickness (mm) 0.3 0.3 0.3 0.3 Inner LinerLayer Used Blend Example Example Example Example Blend 1 Blend 1 Blend 1Blend 1 Second Layer Thickness (mm) 0.1 0.1 0.1 0.1 Layer Used BlendExample Example Example Example Blend 7 Blend 8 Blend 9 Blend 10Buttress Thickness Ratio Gs/Gb 0.5 0.5 0.5 0.5 Portion Thickness Gs (mm)0.2 0.2 0.2 0.2 Performance Weather Resistance (index) 114 127 127 105Evaluation Flection Crack Growth Test (index) 132 150 140 120 Static AirPressure Decreasing Ratio 2.7 2.7 2.7 2.7 Rolling Resistance (index) 102102 102 102 Overall Judgment A A A A

TABLE 8 Comparative Comparative Example Example Example Example 3-6Example 3-10 3-11 3-12 3-13 Constitution of First Layer Thickness (mm)0.3 0.3 0.3 0.3 0.3 Inner Liner Layer Used Blend Example Example ExampleExample Example Blend 4 Blend 4 Blend 4 Blend 4 Blend 4 Second LayerThickness (mm) 0.1 0.1 0.1 0.1 0.1 Layer Used Blend Example ExampleExample Example Example Blend 5 Blend 5 Blend 5 Blend 5 Blend 5 ButtressThickness Ratio Gs/Gb 1 0.75 0.65 0.55 0.4 Portion Thickness Gs (mm) 0.40.3 0.26 0.22 0.16 Performance Weather Resistance (index) 136 136 136136 136 Evaluation Flection Crack Growth Test (index) 118 140 155 160124 Static Air Pressure Decreasing Ratio 2.7 2.7 2.7 2.7 2.8 RollingResistance (index) 101 102 102 102 103 Overall Judgment B A A A A

It is noted that in Tables 7 and 8, the values of the layer thickness ofthe first layer and the layer thickness of the second layer eachindicate an average thickness from the tire crown portion to the beadportion except the buttress region (Rs).

<Performance Test>

For each of the pneumatic tires manufactured as described above, thefollowing performance test was conducted.

<Weather Resistant Test>

The inside of the tire inner liner was subjected to a weather resistancetest using a Sunshine Super Long-Life Weather Meter provided by SugaTest Instruments Co., Ltd. under the following conditions. Each innerliner was irradiated for 60 hours under the conditions at a bath insidetemperature of 63° C., at a humidity of 50%, at 60° C., and withrainfall for 12 minutes. The number of cracks in the inner liner afterthe test was obtained. With Comparative Example 3-1 being regarded as areference, relative values of the number of cracks of other ComparativeExamples and Examples were obtained, and a weather resistance index wascalculated based on the following expression. As the value is larger,the weather resistance is more excellent.

Weather Resistance Index=(the Number of Cracks in Comparative Example3-1)/(the Number of Cracks in Each Example)×100.

<Flection Crack Growth Test>

In endurance traveling test, evaluation was made depending on whetherthe inner liner was cracked or detached. Each trial tire was assembledto a JIS specification rim 15×6JJ. The tire internal pressure was set at150 KPa, which was lower internal pressure than normal internalpressure. The load was set at 600 kg. The speed was set at 100 km/h. Thetravel distance was set at 20,000 km. The inside of the tire wasobserved to measure the number of cracks and detachments. WithComparative Example 3-1 being regarded as a reference, crack growth ineach Comparative Example and each Example was indicated by an index. Asthe value of the index is larger, the flection crack growth is smaller.

Flection Crack Growth Index=(the Number of Cracks in Comparative Example3-1)/(the Number of Cracks in Each Example)×100

<Static Air Pressure Decreasing Ratio Test>

A 195/65R15 steel radial PC tire produced by the above-described methodwas assembled to a JIS specification rim 15×6JJ, and air was introducedthereinto at an initial air pressure of 300 Kpa. Then, the tire was leftfor 90 days at a room temperature. Then, the air pressure decreasingratio was calculated.

<Measurement of Average Thickness>

The 195/65R15 steel radial PC tire was equally divided into eight in thecircumferential direction. In each of the divided portions, eight cutsamples were made by cutting it in the tire radial direction with awidth of 20 mm. For each of the eight cut samples, the thickness of theinner liner was measured at five points with an equal interval in eachof buttress region Rs and bead region Rb. Arithmetic mean values of themeasured values at the total of 40 points each were determined as Gs andGb, respectively.

<Rolling Resistance Index>

Each trial tire was assembled to a JIS specification rim 15×6JJ, and arolling resistance tester provided by Kobe Steel Ltd. was used tomeasure rolling resistance thereof while performing traveling at a roomtemperature (38° C.) under the conditions of a load of 3.4 kN, an airpressure of 230 kPa, and a speed of 80 km/h. Based on thebelow-described equation, the rolling resistance change ratio (%) ofeach Example was indicated by an index with Comparative Example 3-1being regarded as a reference 100. It is shown that as the rollingresistance change ratio is larger, the rolling resistance is furtherreduced.

Rolling Resistance Index=(Rolling Resistance of Comparative Example3-1)/(Rolling Resistance of Example)×100

<Overall Judgment>

A tire that satisfied all of the following conditions was judged as A.

(a) weather resistance index of more than or equal to 105;

(b) flection crack growth index of more than or equal to 120;

(c) static air pressure decreasing ratio of less than 2.7; and

(d) rolling resistance index of more than or equal to 105.

A tire that satisfied any one of the following conditions was judged asB.

When plural judgments applied, a lower evaluation was adopted.

(a) weather resistance index of less than 100;

(b) flection crack growth index of less than 120;

(c) static air pressure decreasing ratio of more than or equal to 2.7;and

(d) rolling resistance index of less than 105.

INDUSTRIAL APPLICABILITY

The pneumatic tire of the present invention can be used as a pneumatictire for track/bus and a pneumatic tire for heavy vehicle, besides apneumatic tire for passenger car.

REFERENCE SIGNS LIST

1 pneumatic tire; 2 tread portion; 3 sidewall portion; 4 bead portion; 5bead core; 6 carcass ply; 7 belt layer; 8 bead apex; 9 inner liner; Rbbead region; Rs buttress region; Le tire largest width position; Lt beadtoe; Lu corresponding position at belt layer end; PL polymer layerstack; PL1 first layer; PL2 second layer.

1. A pneumatic tire comprising an inner liner disposed on an inner sideof the tire, said inner liner being composed of a polymer sheet made ofan elastomer composition containing a SIBS modified copolymer obtainedby modifying a styrene block portion of a styrene-isobutylene-styrenetriblock copolymer with acid anhydride, and in said inner liner, a ratio(Gs/Gb) between an average thickness Gb in a bead region Rb extendingfrom a tire largest width position to a bead toe and an averagethickness Gs in a buttress region Rs extending from the tire largestwidth position to a corresponding position Lu at a belt layer end being0.30 to 0.75.